[FEATURE] Thin API to add global, static TypoScript includes

These inclusions do not show up in the static TypoScript template selector - and thus should only be used for truly global TypoScript which is 1) not susceptible to inclusion order and 2) never needs to or is allowed to be removed by an integrator.

Integrators can still change the TypoScript values included this way - but cannot remove the entire inclusion.

Example usages:

```
Tx_Flux_Core::addGlobalTypoScript('EXT:myext/Configuration/TypoScript/');
Tx_Flux_Core::addGlobalTypoScript(array(
    'EXT:myext/Configuration/TypoScript/',
    'EXT:myext/Configuration/OtherTypoScript/'
));
```

...which will load `setup.txt` and if it exists, `constants.txt` from the provided location or locations, same as when including traditional static TS.

Since there is no display in the static TS template selector, inclusions do not require a name - just the location or locations to be included.