lua: remove "lua/" prefix from script names

This affects the return value of mp.script_name, the "client name"
(what's returned by mpv_client_name()) and all associated features, as
well as the mpv terminal output module prefix when scripts print
something.

As discussed in #748.
input: increase number of maximum sections

This is because Lua scripts creating key bindings create 2 input
sections per script.

Probably fixes #759.
client API, video: signal reconfig at the right time

Filter reconfig can now happen a few frames before VO reconfig.