Move core parts of KexiDB lib from kexi/kexidb to calligra/libs/db (libcalligradb) for reuse by Word's Biblio module

* GUI- or Kexi-related bits such as validators are still in Kexi
* Only the SQLite3 driver is moved to libcalligradb, others stay within Kexi
** thus, calligra libs depend on the driver, i.e. depend on SQLite3 (this was the case already for Words and Kexi)
** calligra libs depend on ICU as well for proper unicode handling (which is dependency of Qt 5 anyway)
* Predicate library, as a Qt-only component, will replace functionality of the calligradb lib
* sqlitedump tool used for database for interactive database compacting stays in Kexi; if needed could be moved to libs/ too
* a few functions from libkexiutils moved to libcalligradb, so libkexiutils is not dependency
* for simplicity/API stability, namespace stays as KexiDB
* README.PACKAGERS file updated

REVIEW:105464
DIGEST:Kexi's data handling library KexiDB become common component of Calligra.