Update translator documentation accordingly.

Probably a few cases left where "tag[ged[" has to be replaced by "list[ed]".

L10n/i18n updates.
Superfluous whitespace removed.
Add FIXME for a few i18n issues I couldn't solve this quickly.

Takes care of documentation for all core code added in merge of "people tags" feature (Commit:e75c9988).

- fix <activity:subject> generation so we get the profile info (what's available so far)
- use id instead of nickname for group join/leave forms so we can join/leave remote groups
  while the rest of the groups UI remains limited to local groups
  (plugins are responsible for making sure remote notifications and permission checks are done)
- fix remote notification when joining group through OStatus's remote subscribe form

This is the first pass at a group home page.