Cleanup MIDebugger output signals

Summary:
There are 4 signals used for various output from the debugger:

• applicationOutput: emitted when got stream record from the 'target' channel
• userCommandOutput: emitted when got stream record from the 'console' channel and it's a user command
• internalCommandOutput: emitted when got stream record from the 'console' channel and it's not a user command
• internalOutput: emitted when got stream record from the 'log' channel or stderr from the debugger

And there are 2 output toolviews when debugging.

• The normal Debug Output panel controled by MIDebugJob
  • Shows applicationOutput, via MIDebugSession::inferiorOutputLines
  • Shows internalCommandOutput, via MIDebugSession::debuggerInternalCommandOutput
• The GDBOutputWidget which is part of the GDB plugin
  • Shows userCommandOutput, via MIDebugSession::debuggerUserCommandOutput
  • Shows internalCommandOutput, via MIDebugSession::debuggerInternalCommandOutput
  • Shows internalOutput, via MIDebugSession::debuggerInternalOutput

This should match the old behavior for toolviews and fixes the testStdOut unit test.

Test Plan: gdb unit tests

Reviewers: KDevelop, apol

Reviewed By: KDevelop, apol

Subscribers: kdevelop-devel

Differential Revision: https://phabricator.kde.org/D2175