Split existing rules into separate rulesets

[saberzero1]

Closes #26

• Split up the five commands messages into five rules under command/
• Split up the four settingsTab messages into two rules under settingsTab/
  • I decided to combine settings, general, and pluginName, as these are all relevant for the heading text content. (no "settings", no "general", and no plugin name in heading respectively".
  • The other rule, no-manual-html-headings, can now be automatically fixed with --fix due to the split.
• Moved the vaultIterate rule into vault/iterate, as there will probably be more vault-related rules. (Perhaps this rule should be moved to vault/.