QmlProfiler: Don't rebuild the same key list over and over when saving

Saving a trace is so much faster like this.

Task-number: QTCREATORBUG-11823
Change-Id: I5c68a16739d8bc49bfc0e3bb923ab23058aab6d0
Reviewed-by: Kai Koehne <kai.koehne@digia.com>
QmlProfiler: Avoid indexOf and contains on list of strings

The iteration and comparison done by that takes significant time for
large traces.

Task-number: QTCREATORBUG-11823
Change-Id: I706b42f64ef0fd8b89229f51e52f0faaaf61d87a
Reviewed-by: Kai Koehne <kai.koehne@digia.com>
QmlProfiler: Make sure only hovered events are selected

Task-number: QTCREATORBUG-11824
Change-Id: Ib471f2a04b37e159fb7876e7f5c94ad3e8f368a9
Reviewed-by: Kai Koehne <kai.koehne@digia.com>