core: Show error message in admin when a module fails to start

e.g. when it is missing any dependencies

(cherry picked from commit 8f0b9456a7aa1a755e1f12ee98b5216f96356188)

Conflicts:
	src/support/z_module_manager.erl
doc: Update mod_twitter to show how to do Twitter login

(cherry picked from commit 7429749ed77e3e0dc74b84ff068e6877a5b07144)