(feature): use org-capture templates

[jethrokuan]

Instead of implementing our own templating system, we abuse org-capture's templating system. We add 2 additional properties:

1. :head: a starting template that goes at the beginning of the file.
2. :file-name: a string that expands to the file id

It's really hacky, but it works:

In addition, org-roam-capture works for org-protocol:

Motivation for this change

#191