Save and Load 'projects'

[ollisco]

The IDE should be able to save and load projects

Required Functionality:

• The saving function saves the current state of the project including asset- and entity information

Desired functionality:

• The project can be placed anywhere on the computer (including paths with spaces or non-ASCII chars)

[lukasfri]

Adding to this, we should implement some type of "level"-file format which saves entities that are in a level etc.