LibreSignage v1.2.0 release

LibreSignage v1.2.0 is finally here! Even though this release isn't very
big in terms of new features, some important bug fixes are included. Users
of LibreSignage v1.1.0 are encouraged to upgrade as soon as possible.

Changelog for v1.2.0.
  - [bugfix]   Fix a bug where markup [containers] weren't 100% high by default
               which caused some problems with slide layout.
  - [internal] Rewrite most web interface JavaScript files and clean them up.
  - [docs]     Add JSDoc documentation to web interface JavaScript.
  - [docs]     Improve documentation about Docker and about reverse proxy config.
  - [feature]  Implement support for passwordless users.
  - [feature]  Implement a bootstrap page for automating passwordless logins.
  - [bugfix]   Fix a bug where non-admin users couldn't change passwords.

Huge thanks to everyone who has contributed code, submitted issues, suggested
new features or just used LibreSignage.
This tag has no release notes.