Optimize Shared-Pointer Usage

So far our API and codebase passes shared pointers by value. This should be made const& to optimize the superflous refcounting in such cases. This was also mentioned in one of the talks here: http://channel9.msdn.com/Events/GoingNative/GoingNative-2012 I (milian) will try to find out which one it was if anyone doubts the above statement.

Improve Session-Workflow

Beautify/redesign the "pick session" dialog ("kdevelop -ps")

Prevent .kdevduchain leakage

Some unit tests, maybe even temporary sessions in general, allocate a .kdevduchain session cache but never clean that up, leading to a huge mess there... It should also be tested whether this can happen if users create temporary sessions for debugging ("kdevelop -d ..."). And of course it must be asserted that the cache gets removed when a session gets removed.

Leverage Plasma for Welcome-Screen

Aleix worked on this in his GSOC, someone should pick that up and finish it properly.

Refactor Project Filtering

Centralize filtering of project files, share code between managers. Take generic-manager as basis.