Doc: Split up the "Working in Edit Mode topic"

- Make topics shorter and easier to browse
- Move information around
- Delete duplicate how-to topics
- Add \sa links to how-to topics

Task-number: QTCREATORBUG-29361
Change-Id: Ie84a29993129d175bbd65143fcfc45aa8304d621
Reviewed-by: Eike Ziller <eike.ziller@qt.io>

doc/qtcreator/src/user-interface/creator-only/creator-how-to-switch-between-modes.qdoc

@@ -37,7 +37,7 @@
         \li \uicontrol Edit
         \li \key Ctrl+2
         \li Edit project and source files.
-        \li \l{Working in Edit Mode}
+        \li \l{Edit Mode}
     \row
         \li \uicontrol Design
         \li \key Ctrl+3

doc/qtcreator/src/user-interface/creator-only/creator-reference-sidebar-views.qdoc

@@ -65,7 +65,7 @@
     incoming calls.
 
     Select the \inlineimage icons/languageclient.png
-    button on the \l{Managing Language Servers}{editor toolbar}, and then select
+    button on the \l{Edit Mode}{editor toolbar}, and then select
     \uicontrol {Restart} to collect call hierarchy information for the function.
 
     \image qtcreator-call-hierarchy-view.png {Call Hierarchy view}