issue 564: fix imports

issue 564

Empty folders are automatically skipped when browsing repository tree  (similar to github "folder jumping" feature).

GitBlit no longer uses Google charts

Formerly by default the PluginMaganer would support no proxy setting.
For servers behind firewall and HTTP proxy this would prevent installation of gitblit plugins.

When configuring a different top-left logo, we would like to allow
to have a different HxW aspect ratio image. We need then to avoid
locking down the height of the logo and just keep the existing aspect
ration as-is.

When a manager is injected through other means, (e.g. using a different
GuiceModule and injector in Gerrit) we need a way to start it without
having to necessarily passing through the injection process again.

This property allows the administrator to hide the user related part of
the top panel. This can come handy if there's no use for it (i.e. if
Gitblit runs as Gerrit plugin).

Ticket reporters should be able to specify severity whereas only those with repository push access should be able to specify priority. This also fixes a bug related to non-admin users creating tickets.

Usability bug fix

If the opacity slider was moved to the far right faster than the
animation showing the image, the user would never see the old file
because opacity got adjusted right away.

Now we first move the overlay slider to the right, so that something
is visible, and then quickly animate opacity to the current value.