User defaults and presets

[pfebrer]

Give the possibility to users to add their global defaults (probably stored in a file inside sisl.viz, although then it would have to persist through updates) and local defaults (stored in a file in the specific plot).

I think defaults would be mainly stored in a dict where the first level keys are the plot classes.

It also would be nice to let the user have presets. In this way, users would be able to reference them in the splot command (#8), for example.

[pfebrer]

The presets part is done. Users can define their presets in the path defined at sisl.viz._user_customs.PRESETS_FILE ("~/.sisl/presets.py" by default). This file should define a variable called presets containing a dict. Each key of the dict defines a preset, so users can have as many as they want. They are automatically accesible everywhere (python, CLI, GUI).

[pfebrer]

So

• presets
• defaults