Miscellaneous project cleanup

These changes clean up a few issues with the project structure and organization that I noticed after checking out and attempting to build the project. Namely, it makes the following changes:

* Removes and ignores `.DS_Store` files
* Updates the MtProtoKit submodule (the previous tree could not be checked out)
* Fixes framework and library search paths (which were previously hardcoded, instead of being project-relative)
* Removes and ignores `.xcarchive` files
* Removes executable bit from text files