src: clazy compiler warnings

get rid of most clazy warnings (https://github.com/KDE/clazy)
* range loop use refs
* qcolor ctor with ints
* missing Q_OBJECT macro
* use .constfirst instead of .first

enabled ccache for unix systems for fasterr recompiling
* if ccache is in path we use it now

src/lib/data/fulltextsearch/FullTextSearchIndex.cpp

@@ -26,7 +26,7 @@ std::vector<FullTextSearchResult> FullTextSearchIndex::searchForTerm(const std::
 
 	std::vector<FullTextSearchResult> ret;
 	FullTextSearchResult hit;
-	for (auto f : m_files)
+	for (auto& f : m_files)
 	{
 		hit.fileId = f.fileId;
 		hit.positions = f.array.searchForTerm(term);