Understand/improve helper installation/check

On Linux, we need the helper bitmask-root and the polkit policy file. Let's handle this, if we merged !171 (merged) and !172 (closed)

Current situation:

  func (b *Bitmask3) InstallHelpers() error {
      // TODO use pickle module from here
      return nil 
  }

• InstallHelpers() is exported via pkg/backend/api.go
• the cpp code maybe runs the function

gui/main.cpp
190:    bool installHelpers  = parser.isSet("install-helpers");
211:    if (installHelpers) {
213:        InstallHelpers();

Desired behviour

• Go code should only check if both files are there
• not part of the Go code:
  • install helper
  • dev: install helpers via Makefile
  • prod: install helpers via package
  • current: Code asks user for sudo password...
• Remove InstallHelpers from Bitmask interface
• During start: check if bitmask-root + policy file exists (maybe in the Bitmask3/5 struct initialization)
  • exit? if the helpers are not there