feat!(journal): periodic & multiple journals

[benlubas]

implements #1471

Features

• Support for multiple journals, and periodic journals
  • Each journal gets a name, start date, time period, and file format string/stategy
  • you can specify period as either days or months + years.
• Ships with a daily, weekly, and monthly journal by default
• users can create their own journals
• all the journal commands now optionally take a journal name. When the name is left out, uses the default journal (configurable, defaults to daily).
• new commands, :Neorg journal previous|current|next <journal_name>
• each journal gets it's own template

Of Note

• looking for feedback on:
  • functionality--does this cover all the cases we want? Does this ship the defaults that we want?
  • user experience/configuration--anything else that should be configurable? Should each journal be able to have its own folder? or should they continue to be in the same overarching folder, with configurable subfolders/the option to not be in a subfolder?
• TOC code is untouched and untested, I think forcing each journal into its own subfolder would make the TOC implementation easier, other suggestions on how to handle it would be welcome
• The breaking change is pretty minimal right now. Templates are now configured differently, and templates files will have a new name. Instead of configuring with template_name = template.norg it's now base_template_name = "template" and templates files will be created on a per-journal basis like: template-daily.norg

[benlubas]

@maxkuzn if you have feedback on the features here that would be great