[MapEditor] Refactor Offset-calculation in class 'MapSelection'

- To make the code more readable
- Centralized call to Math.min(..) and made he minimum-calculation easily replaceable
Refactoring of class 'MapSelection' to hide internal implementation details
Merge pull request #78 from Kadmian/develop

[MapEditor] Refactor class 'MapSelection' to hide implementation details
[Client] Added missing a star implementation
[Client] Removed path finding algorithm interface with wrong file casing
[Client] Readded path finding algorithm