[danoli3]

Fixes #602.

On every launch and every Settings tab click the GUI asked the cmdline --getofpath and replaced the OF path with the answer, and saved it. With the app outside an OF tree (e.g. /Applications) the answer is ../../.., so a path set in Settings was lost on the next launch.

• picking the path with the folder dialog or typing it sets ofPathManual in settings.json
• launch / Settings tab: a manually set path that is an openFrameworks folder (absolute, has libs/openFrameworks and addons) is kept; otherwise detection applies as before
• detection never replaces a valid OF path with one that isn't (../../..)
• the ofPath button still re-detects and clears ofPathManual

Tested with the GUI (scratch OF tree, detection finds that tree): saved /Users/.../openFrameworks with ofPathManual: true -> kept (keeping manually set path), with false -> detected path used and saved.

[danoli3]

Combined into #683.