Include workspace con in workspace event

Send the affected workspace in the "current" property for each workspace
event for any type of workspace event that affects a particular
workspace.

fixes #1411
Fix start_application() doc about which shell is used

Since this commit:

f691a55923850a4d315450925fc98733d07b69c9

the shell that is used is the system's bourne shell (/bin/sh) and the
env variable SHELL is not considered.

No logic changes.
Merge remote-tracking branch 'i3-original/next' into gaps-next