Use request type constants everywhere
Each entry point (application) now defines the actual
request type at a very early point of the request, so
each call within TYPO3 can use the predefined constants
at all times.
Previously this was done within the Bootstrap after loading LocalConfiguration.php etc, and by evaluating other
parameters to detect which RequestType should be used.
By directly setting the option within each application, the
constants "TYPO3_enterInstallScript" and "TYPO3_cliMode" can be removed, as well as $GLOBALS['TYPO3_AJAX'].