events: make wit_eventarray_add take va_list

rename former wit_eventarray_add to wit_eventarray_add_vl and
create new wit_eventarray_add as a wrapper around va_list one.
events: fix compilation warrning

bad cast
events: fix extra format argument

in this dbg message left one extra format argument
server: create aliases for opcodes

It is confusing for all actions from client to call process_request.
Create aliases called by opcodes.
global: add EVENT_EMIT operation

this one only sends opcode. Also reorganize code.
server: add EVENT_EMIT to process_request

so that we can handle this operation
client: add trigger_event action

this function will send an event via socket to the display and
waits for it to be emitted (sent to dispaly's fd, not ran)
tests: test EVENT_EMIT operation

only pointer button event for now..