tests: Build tests into separate executables

Allow selectively run single test cases and produce useful reports on
the pass/fail ratio.
tests: Add make check target

The testfiles directory is renamed to match installation path and so
allow executing tests from build directory.
tests: ServerSessionHandlerTest: set DB file path

Broken since ec17dfc (moving to development on meego.gitorious.org) when
the default path moved from /tmp/... to /etc/... (permission denied).
tests: SessionHandlerTest: fix cleanup routine

Broken since 70864c5 ([buteo-syncml] Fix profile removal - set absolute
file path when calling setDatabaseFilePath())
tests: SyncAgentTest: Fix library reference for Qt5
tests: update ServerSessionHandlerTest

Broken since 135a4c6 ([buteo-syncml] Use slow sync if preferred by sync
agent)
NonceStorage: Fix typo in SQL query

[buteo-syncml] NonceStorage: Fix typo in SQL query