Patch v0.15.1 — Rocket Science Steam update #143062

Fixed some issues found by @Gigantoherceg, @Pietrus1745 and @olafoertelt, Release notes v0.15.1 Features: staff cell will be marked if worker is not yet assigned to any building; Changes: reworked main menu a bit; Known issues: game stuck when pressing "Continue" button in the Main Menu after all saves were deleted; wrong description for "Turn on lights" contract; missing param in the description for "Put spacecraft into geostationary orbit" contract; improved base tutoril step where you turn on engines after time warp, so engines will explode less frequently; wrong parameter for "Leave Earth's SOI" contract.