Add a base config file

The user config is recursively merged into the base config. This enables
to put reasonable defaults in a single place while still being able to
overwrite everything.
Move element_style and curve_style to base config
Extend element_style, curve_style config

Move some arguments into the config that were previously hardcoded.
Fix use of obselete signature of cpymad.madx.match
Replace Vector by simple dicts with 'x','y' keys

The 3-axis case (s, x, y) is handled much better by this. For the rest
of the cases, it might be less idiomatic to use dicts instead of tuples
but it is more consistent internally.
Read s/x/y units from config
Merge branch 'base-config'