Add "File Converter" Editor to IGDE

[LordOfDragons]

By adding new file format modules it might be desirable for users to work in versatile but less optimal formats (like FBX, complex loading, large files) converting to higher performance formats (like demodel, fast loading, small files).

All file loading modules are required to also support writing (although not all can yet). Doing file conversation is thus simply a matter of writing files to a different filename in C++.

To help with this process adding a file converter would be useful. This avoids the need to compile against libdragengine.so to do file conversation. The editor should support two modes in the first version:

1. Convert a single file to a different file name which can be anywhere (precise conversion)

2. Convert all files matching file extension in a directory to a specified format. The target filename is the source filename with the extension switched to the desired format. (bulk conversion)

[LordOfDragons]

Idea from Deadlytoad: Allow models (for example *.fbx) to be converted not only into another model (like .demodel) but also into navigation spaces (.denavspace). This would allow developers to use whatever 3D application they want to use, export to FBX and convert the FBX to a navigation space. Needs a way to assign navigation space type numbers (aka unsigned short) to model textures (which are named). Could be a little dialog for example with a list of model textures and the type number to assign. More is not required.