detect sound player on first start as soon as gajim is started, not first time we open preferences window. Fixes #3566

don't request jabber:iq:last and jabber:iq:version to real jid in a (semi) anonymous room, even if we're moderator and we know the real JID. Fixes #3454

Quick fix: What does not exist cannot support anything. Fixes #4031.
Fix variable referencing. Fixes #4076.

We don't match all valid URIs like blub:blaa but include common used (non)-urls like www.google.de

* Coding standards
* remove useless key-list creation

Make nick completion sorted  case-insensitive. Fixes #4063. (was already IMO)
Restore #2975 way. Last nick that highlighted us are first. Fixes #2975.

Remove some usage of has_key() in the contacts module. It is a bit slower (method overhead) and will be deprecated soon.
In roster_window. make a small if-clause more pythonic.

Correctly count metacontacts in non merged accounts mode if we have metacontacts over several accounts.

Remove timing information for roster drawing.

implementing a later coming fallback to disco rather easy.

Caps is now used for: File Transfers, MUC Invites, Ad-Hoc Commands.

TODO:
 * Also handle it this way for typing notifications
   (This might give some trouble / compatibility issues)
 * Fall back to service discovery if no caps are available. Otherwise,
   we break compatibility with a lot of clients. (Asterix?)

This also fixes the problem of showing the wrong icon when expanding metacontacts.

Example:
We have the groups A, B, C in our child model
But only A and C are visible (and therefore in modelfilter)

Imagine we have a childIter_G pointing to group B
Getting its path in the childmodel, will give us (lets say) 2
2 means now the second group/row in the CHILD model
We now pass this to the tree and tell him "Expand row 2"
The tree itself is looking at the 2nd row of modelfilter: "Hey modelfilter, expand row number 2"

For modelfilter row number 2 is C and NOT B

We are not absolutely sure why some things are happening. Maybe that will help tracing the strange bugs.