Added graph, date snippets, and experimental support for plugins

New features:

• Added Foam: Show Graph command
• Added date snippets (/+1d, ...) to create wikilinks to dates in daily note format
• Added Foam: Copy to Clipboard without brackets command

Improvements:

• Added new option to not generate wikilink definitions foam.edit.linkReferenceDefinitions: off

Bug Fixes:

• Daily note could be created before the daily note directory (#232)
• Fix issue with janitor crashing when file is only frontmatter (#222)
• Fix link references spacing when there is no trailing newline (#236)

New experimental features:

• Introduced foam local plugins