Project tree improvements

This patch provides a few improvements:
#### 1) Possibility to define color of library by theme with distinguish: 
* Library
* IncludeLibrary
* ExternalLibrary
```
ProjectTreeView.ForeColor.Library=#0000FF
ProjectTreeView.ForeColor.ExternalLibrary=#00008B
ProjectTreeView.ForeColor.IncludedLibrary=#008B8B
```
Solution is backwards compatible, if there is no definition in Theme, then will be used `Color.BLUE`

This is useful with dark themes. [VsThemeDark](http://www.flashdevelop.org/community/viewtopic.php?f=20&t=11974)
before:
![demo_before](https://cloud.githubusercontent.com/assets/4076929/5425610/4ed3b98c-831f-11e4-8836-fe751c4ec107.PNG)

after:
![demo_after](https://cloud.githubusercontent.com/assets/4076929/5425609/4a3434ec-831f-11e4-8fd2-55d1e1824b37.PNG)



#### 2) Add possibility to add a directory as a library for AS3 project. 
#### 3) Set color for included directory according to type of include. In addition included directory has different icon.
demo:
![demo](https://cloud.githubusercontent.com/assets/4076929/5425612/56db1620-831f-11e4-84f2-76c64544dba0.gif)