Summary:
- QSignalMapper can mostly be replaced using straightforward
  lambdas, reducing the code size

Test Plan:
- switch scope and arrangement of problems in ProblemView
- create an application using the AppWizard
- add a compiler
- switch representation of register variables
- add code to an existing file using a file template
- open a file with an external application
- switch to header/source file using the context menu action
- track changes of a variable in the debugger
- status bar seems to work
- untested: runcontroller

Reviewers: #kdevelop, mwolff

Reviewed By: #kdevelop, mwolff

Subscribers: mwolff, apol, kdevelop-devel

Differential Revision: https://phabricator.kde.org/D9881