Register settings field for keyword search.
Keyword search should be on by default.

The option to enable/disable keyword search was added for 0.7.4. This
settings is enabled by default. If upgrading from a previous version,
this will make sure upgrades are also enabled by default.
Convert the settings updates to a switch statement.

Had if/elseif logic in place but that wouldn't work as expected.
Move initOptions call to initDependencies().
Remove double semi-colon.
User keyword setting to determine if keyword search should be performed or not.
Removed use of deprecated cnOptions::getSearchUsingFulltext() call.
Remove deprecated cnOptions::getSearchUsingFulltext() method.
Ensure keyword search is enabled if user decides to try to disable both search methods.
Update keyword search setting description.