* DwarfTree.cs: - basic implementation of the underlying tree
  structure
- supports adding and removing nodes

* dwarfkeeper.csproj: - re-adding to solve annoying inclusion issues

* dwarfkeeper.sln: - re-adding to solve annoying inclusion issues (and
  contains no user specifics so shouldn't hurt)

* .gitignore: - updated to add .sln and .csproj to version control
  (they do not contain user specifics)