This adds a PackageBases table to the database schema and moves the
following fields from the Packages table to PackageBases:

* CategoryID
* NumVotes
* OutOfDateTS
* SubmittedTS
* ModifiedTS
* SubmitterUID
* MaintainerUID

It also fixes all database accesses to comply with the new layout.

Having a separate PackageBases table is the first step to split package
support. By now, we create one PackageBases entry per package (where the
package base has the same name as the corresponding package). When
adding full support for split packages later, the package base name will
be derived from the pkgbase variable and a single package base will be
shared amongst all packages built from one source package.

Signed-off-by: Lukas Fleischer <archlinux@cryptocrack.de>