Added a utility method for creating workspace selection dialogs to UIUtils
ProjectLoadPath shouldn't assume that IProjects can all become ICoqProjects
Expose the registered providers through the AbstractLoadPathManager API
Finished the initial implementation of LoadPathConfigurationPage

There's rather more code duplication than I'd like, and the system library
functionality isn't implemented yet, but this is an excellent start
Removed support for manually generating Makefiles for Coq projects

The Coq project builder will soon unconditionally generate a Makefile as
part of the normal build process
Added a new, slightly cleaner dependency tracker implementation

This new class is called DependencyTracker2 at the moment, but it'll
replace DependencyTracker completely in a few commits' time
Removed the modification timestamp check from CompileCoqRunner

The builder will soon perform its own timestamp checks
Removed the Makefile generation code

This will shortly reappear as part of the new build process
Rewrote the Coq project builder to behave more like make

All objects are now always considered as build candidates whenever the
builder is invoked, and those build obligations are discharged according to
make-like freshness tests
Always generate a new KopitiamMakefile whenever the Coq builder is invoked

Note that KopitiamMakefiles don't yet take external, abstract, or project
dependencies into account
Removed the old build loop management code
Explicitly order the dependencies when generating KopitiamMakefiles

This should stop the content of KopitiamMakefiles from fluctuating
unnecessarily
Make sure the complete load path is expanded correctly
Don't attempt to clean up output directories that don't exist yet
Don't consider files which don't exist to be up-to-date
Display errors when formerly-resolvable dependencies become broken

This commit also makes a few supporting tweaks to DependencyTracker2
Don't postpone the resolution of ideal dependency paths

Because the builder now selects build candidates in a more intelligent way,
this is no longer necessary -- dependencies can (and should!) be identified
as soon as possible
Renamed the DependencyTracker2 class to DependencyTracker
Bumped the version number to 0.3.7 and added a changelog entry