Make context title and summary changeable (#329)

* Make context title and summary changeable

Closes #30

* Fix checkboxes on context settings page

So...I am new to Qt, and I forgot that checkboxes can have a label.
Duh. Fixed.

* Put context settings in a different place

* Put ReplaceMessage and ReplaceVariable in Utilities

src/core/mainwindow.cpp

@@ -955,6 +955,7 @@ void MainWindow::ReloadAllSettings() {
   app_->album_cover_loader()->ReloadSettings();
   album_cover_choice_controller_->ReloadSettings();
   if (cover_manager_.get()) cover_manager_->ReloadSettings();
+  context_view_->ReloadSettings();
 #ifdef HAVE_TIDAL
   tidal_view_->ReloadSettings();
 #endif