Compilers: Rewrite bulk compilation

Now completely DRY, and
better-parallelized too
Compilers: Port Markdown menu item
Compilers: Move exclusions to correct layer

NodeExecutorBase will compile anything.
CompilerRunner won't save excluded files
to disk.

Fixes preview window for excluded files.
Compilers: Properly separate source map code

NodeExecutorBase no longer uses ProjectHelpers anywhere

Fixes file add order issues in subfolders
Bundles: Use new minification code

Also add source map support for JS minification