changeset comments: attempt to highlight the linked comment

This makes it slightly less confusing to follow a notification link to a page
with a lot of comments.

It is ugly, it seems like it doesn't work reliably, and the fixed top menu makes
target navigation unusable in general...

hide add repository button when you don't have at least write permission in group
ref #730

filter out repo groups choices to only ones that you have write+ access to. Before it was read+ access and you got proper
error saying that you don't have write permissions to group to create repo in. Filtering out the read groups is less confusing for users.
ref #730

Return a list of invlidated keys on mark_for_invalidation func
- log.debug list of invalidated keys

reposcann should skip directories with starting with '.'
some code cleanup, moved all skipping to get_repos function

fixes for issue #731, update-repoinfo sometimes failed to update data when changesets
were initial commits

Group management delegation:
this allows users to become an admin of groups
a group admin can manage a group, change it's name
or permissions. A group admin can create child group
only within a group he is an admin off.

Top-level group can be only created by super admins

Global permission update with "overwrite existing settings" shouldn't override private repositories.
It's to confusing to users, and private repos should be always private

Killed home button. It's a wast of space, and every other major service simply doesn't have a home button. Getting to home can be
always achieved by clicking the Instance title on the left side

make gravatar icon little bit bigger, re-use same img src like on other menu items,
fix styling on unread inbox

top menu: show user menu as a menu option like others, now also with login name

A minor regression: the message count is not clickable ... but it was hard to
hit, and somewhat confusing that different parts of the icon meant different
things.

The new html/css will probably need some review and cross platform testing.

top menu: highlight current menu item - reusing hover

Giving a visual hint where the user 'is' helps navigating and feeling
comfortable with the site.

top menu: use 'Repositories' instead of down arrow

- both to be consistent with other menu items and to give a stronger hint than
two abstract symbols.

html: don't hardcode uppercase texts

_If_ we want uppercase then it should be done in css.

remove comments associated to pull request from single changesets, it's too confusing.
Left are only ones that are status change so we can indicate where the status of this changeset came from

improved extraction of user from changeset when sending notification.
Fallback to repo owner if we cannot get the user

fixed ip restriction tests when runned multiple times.
Added sleep to fix cache issues

set the status of changesets initially on pull request, and make sure we care of version collisions.
Fixes issues #690 and #587