CHANGED: major refactor if ModPackPanes

* Moved similar code from FTBPacksPane and ThirdPartyPane into
  new AbstractModPackPane.java
* Converted private/static variables and functions mostly publics
* Renamed function
* Fixed other classes to call member function instead of calling static
  funtions

TODO:
  * Move most of the constructor code into Abstract class
  * Add more abstract functions and their implementation to achieve TODO bullet 1