[qtcontacts-sqlite] Suppress debug output by default

Previously, warnings and other debug output would be emitted by
default.  This commit changes the behavior so that the debugging
output is only emitted if the QTCONTACTS_SQLITE_TRACE env var is
set.
Merge pull request #67 from chriadam/suppresswarnings

[qtcontacts-sqlite] Suppress debug output by default
[qtcontacts-sqlite] Ensure modifiable details remain modifiable
Merge pull request #68 from matthewvogt/evgeny-fix

[qtcontacts-sqlite] Ensure modifiable details remain modifiable