Revert "Removed unused keystring handler. (#24)"
Keystring packets do appear to be sent in at least one case: when typing with the "shift lock" toggle button enabled (part of the MM toolbar, not the standard iOS keyboard shift key). A bit unclear when sent.
This reverts commit d20864c3d18c89d8a8a5049da4ded09cca5119d3.
Moved keystring handler near key handler
and log keystring content
Apply keysym shift detection to keystring input characters
Handling should be merged with regular key handling.