Find in files: Add setting to allow reset of root directory upon change of project

[kpeters58]

Something that has bitten me many times over the years:

PB remembers the root directory for file searches across projects. Consequently it is very easy to run a search in the "wrong" root directory and not to notice this unless one pays close attention.

We could extract the file path of project files and set it as Find in files root directory if the suggested flag was set.