Use Config nesting in `SapphireTest::useTestTheme()`

Using the Config nesting functionality to restore variables
BUG Remove caching of statements due to risk of instability
This would cause segfaults in rare situations where statements are reused
Merge pull request #3328 from tractorcow/pulls/3.2/fix-mysql-segfaults

BUG Remove caching of statements due to risk of instability
API SS_Filterable, SS_Limitable and SS_Sortable now explicitly extend SS_List
Merge pull request #3344 from tractorcow/pulls/3.2/sslist

API SS_Filterable, SS_Limitable and SS_Sortable now explicitly extend SS_List
BUG Fix PDOConnector issues
Travis support for PDO
ATTR_EMULATE_PREPARES = false breaks some test cases
Enable username sans password
Remove unnecessary semicolons delimiting queries
Merge pull request #3353 from tractorcow/pulls/3.2/fix-pdo

BUG Fix PDOConnector issues
API Use "number" HTML5 type for NumericField by default
Merge pull request #3361 from halkyon/number_type_numericfield

API Use "number" HTML5 type for NumericField by default
Merge pull request #3094 from dhensby/patch-3

Use Config nesting in `SapphireTest::useTestTheme()`