Storing the gloperate-viewer's pluginPath in the config file breaks multiple installations

Both installations write their respective `gloperate::pluginPath()` to the config file (`%APPDATA%/CG Internals GmbH/gloperate.ini` on my system) and read it back on the next launch. Consequently, both try to load each others plugins, which may lead to weird errors and crashes if different versions/compilers are used.

Start by tracing where gloperate::pluginPath() is written to and read from the gloperate.ini configuration file under %APPDATA%/CG Internals GmbH. Determine how separate installations can avoid sharing plugin paths, then verify that each installation loads only its own plugins without the reported cross-version or cross-compiler failures.

Written by the indexing model from the issue text.