add support for detecting dialects

Localize the determination of database dialect to QDjangoDatabase.
QDjango currently assumes the use of native SQL drivers, and
therefore uses QSqlDatabase::driverName() directly throughout the
codebase. With current testing using ODBC drivers the driverName
is no longer sufficient for determining database dialect, so
this introduces a private method allowing to determine dialect
based on more complex criteria.
remove redundant includes/libs
add http.pri for common HTTP test rules
skip threaded test on in-memory SQLite database
make qdjangoscript test use db.pri
QSKIP only has 1 argument for Qt5
run tests against in-memory sqlite database
remove trailing semi-colon
enable "make check"
add CONFIG -= app_bundle for tests
Merge pull request #21 from mbroadst/add-dialect-support

add support for detecting dialects