Rename commands for better using abbrev command calls

[mike4git]

Today it is not possible to use abbreviations in command calls (e.g. bin/console n:p:load)

And if you want to load one single fixture you have to use a different command which is very incomfortable to use.

So best solution atm:
bin/console neusta:pimcore:load-fixtures without argument loads all fixtures
bin/console neusta:pimcore:load-fixtures My\Special\Fixture with argument loads specific fixture

Additionally error message should be clearer to use Symfony declaration name instead FQCN.