Kit: Use FileName for icon path

Change-Id: Ica6cf20c4ae1c7d58386d4970e468a105a3263b3
Reviewed-by: Tobias Hunger <tobias.hunger@digia.com>
Kit: Allow renaming autodetected kits

Also allow changes to the icon while at it.

Task-number: QTCREATORBUG-9787
Change-Id: Id2abbd11f12b7e0f577655932b5b2aac4d3bba7c
Reviewed-by: Daniel Teske <daniel.teske@digia.com>