Fix issues with long project names in the minitargetselector

It's impossible to use very long names and some clipping
occurs due to incorrect size hints on QLabel.
- Made the popup minimum width depend on the longest
project name entered. (it will not shrink)
- The build and run labels have increased minimum size hints.
- Combobox tooltip will be set to the project name as to
  make it possible to expand long names.

Task-number: QTCREATORBUG-1278
RevBy: joao