Implement file tagger/compiler for Xcode XIB files

We need to implement support for compiling xib files. In Xcode projects, .xib files (interface files) are built using ibtool and then copied to the <appname>.app/Contents/Resources/<lang>.lproj/ directory.

ibtool --compile OUTPUT_PATH.nib INPUT_PATH.xib

`--output-format human-readable-text` should probably also be passed for displaying error output, as the default output format is an XML property list.

--warnings, --errors and --notices would also be useful to include. There are a plethora of other options we might want to provide access to, too - check `man ibtool`.

Should we add an "InterfaceBuilder" module, that allows properties to be set like: ib.errors: true, ib.autoUpgrade: false, etc.?