group_concat() does not preserve order of the ORDRE BY rank,
making the ordering quite meaningless for pages inside a file.
The recently introduced combobox to filter on a per file basis
should anyway be prefered than any kind of grouping in queries.
So we just remove the groupings here.
"All files" in the previews tab thus should show the best results
first now, from any files part of the result set.
A GUI option to sort by page instead of rank can be considered.
Most users are not to be expected to be familiar with
sqlite's FTS syntax. It also leads to unnnecessary
arrows in some instances.
So wrap every space separated word in quotes, unless
it's already in quotes. Then we just escape those with
double-quotes.
Not entirely ideal, since we may want to search for 'cake', and look at
a preview for 'cake.txt' even if there is no 'cake' inside.
But this will do for now
Purpose is to seperate certain logic from SQLite and generalize it more.
Even though we only have Sqlite atm, in general the database layers
must be stupid as possible, while QSSQuery should do most of the hard work.
Fixes in Tokenizer logic.
Switched to C++17.
