feat: allow strategies more autonomy in sampling decisions

[pekasen]

ATM: Spider keeps track of whether enough seeds are created.

Solution 1: register more than one function per strategy:

• walk-function
• teleport-function
• condition-function
• recheck_node-function

Other solution (which I favor more at the moment):

• the sampler is still one relatively simple function that is passed:
  • the entire node table
  • the edges of the last iteration's seeds
  • a table which the sampler updates (e.g. to keep track of which nodes are burnt if the sampler might want to do so)
  • the configuration
• the sampler then does it's thing and additionally returns an update for the sampler-table (e.g. nodes that were burnt in the past iteration)