Also added Center to Mission support

Also additional major Mission usability changes

- Positions are bounded to rectangle
- No longer re-centers if thumbs go outside bounds
- ThumbPad moves to meet first thumb position, this prevents
inadvertent movement as you put your thumb down

Add scroll height indicators to Flickable

This reverts commit bf31c808.

The overloaded member signal just hit us, to use it is a pain
but the resuting code is faster and less error prone, so it's
still a good thing to do.
Signed-off-by: Tomaz Canabrava <tomaz.canabrava@intel.com>

Causes UI to hang up

Hamburger: Delete, Delete All, Show all Values

Hamburger: Delete, Delete All, Show all Values

Total hack but it seems to work

There are many ways of iterating over lists in C++/Qt.
In the specific case of QStrings, it is known [1] that using
foreach with const references avoids the creation of new
QString objects in each iteration, reducing the time consumed
by the loops.

[1] https://blog.qt.io/blog/2009/01/23/iterating-efficiently/Signed-off-by: Anselmo L. S. Melo <anselmo.melo@intel.com>