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/CMakeLists.txt

@@ -242,6 +242,7 @@ set(SOURCES
   settings/behavioursettingspage.cpp
   settings/collectionsettingspage.cpp
   settings/backendsettingspage.cpp
+  settings/contextsettingspage.cpp
   settings/playlistsettingspage.cpp
   settings/networkproxysettingspage.cpp
   settings/appearancesettingspage.cpp
@@ -427,6 +428,7 @@ set(HEADERS
   settings/behavioursettingspage.h
   settings/collectionsettingspage.h
   settings/backendsettingspage.h
+  settings/contextsettingspage.h
   settings/playlistsettingspage.h
   settings/networkproxysettingspage.h
   settings/appearancesettingspage.h
@@ -524,6 +526,7 @@ set(UI
   settings/behavioursettingspage.ui
   settings/collectionsettingspage.ui
   settings/backendsettingspage.ui
+  settings/contextsettingspage.ui
   settings/playlistsettingspage.ui
   settings/networkproxysettingspage.ui
   settings/appearancesettingspage.ui