LL-296 Added visuals for writing message.

Added visuals and logic for writing message. The looks correspond to the
ones used in Episode sharing. Moved input validation code into
standalone utility module, made those generally usable. Added template
for selected user visuals (in case of user search and selection). Some
more chnages and tunes. There is more room for generalization,
especially regarding the user select related functionalities. Also a
utility for user searhc helper methods should be considered. it could
store have the logic of determining searchable users, defining a
function that could be used as a source for jQuery UI Autocomplete, that
way it could be possible to also create some caching that would be
globally awailable and all the modules using utility could benefit from
it (if caching proves to be needed).
Removed module from loadables in SystemMessages.

This is mainly used for accessing configuration options and is not
needed in that context.