In the modern template also clean up HTML a bit.

Remove last use of experience icons theme so we can remove it after the old templates have been removed.

# The first commit's message is:

core: move inline JS to assets

# This is the 2nd commit message:

Move assets to assets-dir + PSR-2

+ fix typos and indentation

- Add class pure-button-red instead of overwriting primary
- Create a group of 2 button-elements where one is hollow, useful
to show input-files or error-ids.
- Update templates accordingly

- Add class message-box which combined with .error or .success
replaces errorbox and successbox.
- responsive for rtl

- side-menu button moved to the right
- update responsive menu for rtl languages.

- menu-link span position needs to be adjusted.
- footer should move like the rest of the page (js needed)

Changes default css to adapt the login form.
Need fix: when the user can choose an organization, the layout breaks when opening the dropdown menu.