`reload_extra_files` should accept wildcards

Hi,

My app structure is such that each view in my app has it's own config.json located at ui/<view_name>/config.json.

I would love to reload on modification for each of those JSON files.

Currently, I'm doing, for each view:

reload_extra_file = [
  'ui/<view_1>/config.json',
  'ui/<view_2>/config.json',
  'ui/<view_3>/config.json,
  ...
]

but this is a little cumbersome, since I have to add a new line everytime I add a view to my app (and I tend to forget about it).

We should support wildcards for this kind of use case, something like:

reload_extra_file = ['*.json', '*.js', '*.py', '*.yaml']

@benoitc Is that something you would consider implementing ? I can maybe help with this and create a PR if you let me know where this needs to be changed in the current code.