Style changes part 1

The login page has been styled. And the buttons in the top-right corner are better than ever before. And closes #72.

Soon in a pull request near you: styled password reset pages and more!

See merge request !68

Change board/committee pages

Closes #69 

- Remove JavaScript usage for the board pages and use indexed urls
- Rename the urls of the committee pages
- Add the board url to the menu
- Replace default committtee placeholder image
- Preserve the i18n fields from a base class in the translations util
- Fix adding a CommitteeMembership for a board (they were not shown in the list due to the manager being overridden)
- Fix problems when adding/updating a CommitteeMembership of a user that is marked as chair.
- Translatable committee names
- Translatable roles in committeememberships

See merge request !65

- Use fields instead of fieldset in admin
- Preserve i18n fields from base in ModelTranslateMeta
- Re-enable usage of name for boards

Add docker image

Add a docker image.

Zie dit: @lrijneveld, @gmulder

See merge request !67

Add two age filters in the members admin page

Closes #70

See merge request !66

Change committees to activemembers



See merge request !63

- Update the value of _was_chair in `save`, since `__init__` is not called when you do not get a fresh object from the db.

Merge branch 'master' of gitlab.science.ru.nl:thalia/concrexit into feature/change-committees-to-activemembers

Use ID instead of fragile year

Closes #69

See merge request !64

Mentor achievement on profile (and fixes)

Closes #68.

!61 did not have a admin page for the mentor model.
The __str__ gave an error and the model name was plural instead of singular.

And: the mentorship is now shown on the members' profile pages.

See merge request !62

Squashed commits:
[e05e712] Rename Mentors to Mentorship instead of Mentor
[a694422] Fix PEP
[16ecef4] Add 'mentor achievement' to member profiles
[dd10f23] Fix the string format

Gave an exception when saving the model in the admin
[88717d0] Add admin for the mentor model
[08eb778] Change mentors to mentor (all models are singular)

Add model for mentors

They are not well fit in the committee model, and are necessary when we migrate members in #33.

See merge request !61

They are not well fit in the committee model, and are necessary
when we migrate members.

Newsletter integration

Closes #24. Also fixes #66

See merge request !60

Squashed commits:
[c6cbd24] Remove fuzzy translation
[fd0ec11] Add newsletter app
Squashed commits:
[219ef97] Add newsletter from to settings
[00a2804] Add newsletter app
Squashed commits:
[dc13774[ Fix translations
[26f3bea] Prevent mass deletion from admin and fix add form
[2024827] Rename newsletter_optout to receive_newsletter
[baeb801] Squash migrations
[a8b50e7] Tests for email sending
[1d1f0b1] Move object creation and login to setUp
[3d0fda1] Add tests for newsletters that were not sent
[32e4196] Add more and fix tests
[82e5e6f] Thalia headers on the send page
[0d3b9ad] Send newsletter directly to user in BCC instead of using the mailman list
[8855730] Start writing tests
[8007c19] Add check in model for start and end times
[fbcd91c] Add rendering and sending email code
[507e932] Fix PEP styles
[1432cf0] Use main partner from the partners module
[31708d9] Add newsletter images to static
[299a873] Make frontend preview for newsletter
[e01e3d9] Change end date text
[c5661ba] Make newsletters multilingual
[4dc2579] Add help texts to newsletter fields
[337cf5e] Add introduction field to admin form
[262629b] Add introduction textfield to newsletter
[5a46afd] Re-add CASCADE on delete
[3270015] Add newsletter migrations
[bdb5b96] Add admin for newsletter models
[a613072] Finish models
[2e8946f] Add base files

Make the login page somewhat nicer

Make the login page nicer

See merge request !59