Use trie databases in presage predictor

Use the libmarisa based trie databases in presage predictor. This improves the time and space performance of presage by about a factor of 10, which in practice means that very large predictor databases can be used. Needs the SailfishOS presage fork from here: https://github.com/sailfish-keyboard/presage

The last unfinished commit tries to make presage config user-proof by adding a p-o-s specific config file which is used if the necessary features are not enabled in user or system presage config.

In order to for this to be useful, the presage in distros would need to be compatible and the prediction DBs distributed with presage and/or phosh-osk-stub would need to be converted to the trie DB format. So, this is very much a work in progress.