handle communications

Additional code to handle communications. Contains:

• parsing logic to get information about handles required/produces by each task from task.rec
• change to availSequence to allow ALAP insertion
• CommSequence to handle comms, ItemManager to handle data availability
• new option comms in GreedyAlgorithm to activate all this

Notably missing:

• better way to specify bandwidth (for now it is a global value with --bw option)
• for now default location for all initial items is memory node 0
• include this in (some) other algorithms