Remove webkit as a mandatory run/build-time dependency

[buhman]

Is your feature request related to a problem? Please describe. I originally bought my Prusa printers specifically because, unlike other vendors, there was no "cloud" feature.

It is unreasonable that Webkit is a mandatory build-time/run-time dependency, and it should be possible to compile PrusaSlicer such that all mention of "Prusa Connect" is removed entirely.

Describe the solution you'd like Add a new Cmake option, for example SLIC3R_WEBKIT and/or SLIC3R_PRUSACONNECT. When cmake is given with an invocation such as cmake -DSLIC3R_WEBKIT=OFF, the compiled binaries should have no link/load dependencies on Webkit nor a wxGTK that has webview compiled-in. All buttons and menu options that refer to "Prusa Connect" should be removed if these options are OFF.

Describe alternatives you've considered Stay on 2.7.4 forever.

[gordon-quad]

Not sure what WebView is used for, but if there is an option to just turn off this functionality in full to make wxGTK webkit dependency optional - it would be great.

[l29ah]

2276cedc107d3fd8cfc46d5f05cfe1d663b6b152 first bad commit