Detect external AGLint installations, support for extension settings

[scripthunter7]

Closes #75

Changes:

• When the extension is loaded, it checks whether AGLint is installed locally or globally. If it finds an installed version, it can use it instead of the integrated one. Here's an important TODO, we need to check the AGLint version (below a certain threshold the installed AGLint may be incompatible with the extension - typically if the API ever changes). However, to do this AGLint needs to export its version number, so I would resolve this in a different PR, later (most of the check is already prepared in this PR)
• It is now possible to make settings on the extension, demo:
  
• Simplify and optimize build commands with parallel execution. Watch mode should be improved, see Improve dev build #88 (but also in a different PR)
• Some minor fixes, e.g. in filesystem watcher

Tested on Windows / Linux