Add CSS for hover and a more visible item selection
User: `default` is special too
Cleanup: refactored special users
Cleanup: renamed method/attribute to align semantics
User manager: added method to hide permission-related users
User admin: hide permission-related users
WTF this logic
UserSet: removed unnecessary arguments
Textarea: also allow auto-focusing
Fields: also allow setting as read only
User: defined what a meta user is
User admin: username is read only for meta users
User admin: hide irrelevant information from meta users
User: protect meta users from being deleted
Use select2 dropdown to select a user on admin reports page

part of #252
Replace an old report based on new translations and edits with a new score-based report

part of #252
Add format_date_range template filter
Add paid tasks

part of #252
Add hourly_rate to User model, modify update_rates

part of #252
Adjust rendered summary report data to a new structure

Report tables structure is taken from the sketch in #252.
Summary report data is grouped by month.