support multifundchannel in cl

don't know about other implementations, but clightning supports to fund multiple channels at once in a single TX, saving on fees.
The thing is, compiling the command is a huge pita. Would be awesome to be able to copy the command like you can copy the rebalancing script. Just if you have multiple channels to open of course. 
syntax is:

lightning-cli multifundchannel -k destinations='[{"id":"02ad6fb8d693dc1e4569bcedefadf5f72a931ae027dc0f0c544b34c1c6f3b9a02b","amount":2000111},{"id":"03864ef025fde8fb587d989186ce6a4a186895ee44a926bfc370e2c366597a3f8f","amount":3000111}]'