Skipping parts of a goal

[fhnaumann]

Rewrite the skipping behaviour

1. Use CommandAPI for skip command
2. On the website: Configure how many jokers may be used
3. Add a joker item to the players inventory that performs a skip and is used up. Alternatively mimic that same behaviour if /skip [goalname] is typed
4. Add a new command /forceskip [goalname] to just skip without using a joker (if it is unobtainable, for example)

[fhnaumann]

skip (equivalent to using a joker):
/skip -> if only one goal: skip part of goal; if more: error
/skip [goalname] -> if exists: skip part of goal; if not active/does not exist: error

forceskip:
/forceskip -> if only one goal: skip part of goal; if more: error
/forceskip [goalname] -> if exists: skip part of goal; if not active/does not exist: error