Revert #1019 to fix nvim artifacts and flickering.

[PhilRunninger]

Description of Changes

Closes #1020.

Revert #1019, which too liberally used the :mode command in Neovim. This resulted in excessive flickering of the screen. It also caused artifacts on the screen, which ironically were cleared by manually issuing the :mode command.

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New Version Info

• Derive a new version number. Increment the:
  • MAJOR version when you make incompatible API changes
  • MINOR version when you add functionality in a backwards-compatible manner
  • PATCH version when you make backwards-compatible bug fixes
• Update CHANGELOG.md, following this format/example:

  #### MAJOR.MINOR...
  - **.PATCH**: PR Title (Author) [#PR Number](link to PR)
  
  #### 5.1...
  - **.1**: Update Changelog and create PR Template (PhilRunninger) [#1007](https://github.com/scrooloose/nerdtree/pull/1007)
  - **.0**: Too many changes for one patch...