Select shortcuts and color for timeline animation playback

Animation playback has a new looping function that the user can manipulate by clicking and dragging the timeline toolbar and timeline animation bars.

To use this you need to use modifiers while using left mouse button. I have selected ctrl and shift as placeholders for testing purposes so these should be changed to dedicated ones if necessary.

The color for the looping area should be set too.

https://codereview.qt-project.org/c/qt-creator/qt-creator/+/364247

timelinemovetool.cpp

• line 77

timelinesectionitem.cpp

• line 657

timelineselectiontool.cpp 

• line 183
• line 192
• line 199
• line 211

timelinetoolbar.cpp 

• line 324