So far candidates were prefix matched case sensitive which led to
an unfavorable results order.

With this patch, if the input is lower case, the prioritizing happens by
a case insensitive prefix match. Otherwise the match happens case
sensitive (just like before).

Example:

    Search for e.g. "m cppmodelmanager"
    Top result before: AbstractEditorSupport (match at parameter type)
    Top result now: CppModelManager

Change-Id: Ic27042cfe717be812a2237a3437399597c98dd74
Reviewed-by: Orgad Shaneh <orgads@gmail.com>
Reviewed-by: David Schulz <david.schulz@digia.com>