Implementing search feature in map choosers

ref #6374
I've implemented this filter. It looks that it integrates with whole code without disturbing any coherency.. Please share me any thoughts.

My objection in MapChooserLogic.cs:91
```
.Where(m => m.Type == gameMode || gameMode == null)
```
-> the null check was at right (left side is being checked first in logical alternative) so I've moved it to left, and checked this null case - its handling it right now.


![map_filter](https://cloud.githubusercontent.com/assets/6244620/4329867/2aa02052-3fa2-11e4-93dc-3cb5d95c59b7.gif)

![mapfiltercnc](https://cloud.githubusercontent.com/assets/6244620/4329866/2a9f6950-3fa2-11e4-9831-be5df85afa51.png)