Remove the original 'Write' function from the db package and rename the
'WriteMany' function to 'Write' as it can already write one or many Bolt
items to the database.
Also update the test suites and add more coverage in the board package.
Changes:
- Rename the UI type to App.
- Rename NewUI() to NewApp().
- Move init functions to internal/ui/ui.go.
- Call app's initialisation function from main.
- Move the keymapping functionalities to internal/ui/keymappings.go.
- Add documentation for updateColumn() and updateAllColumns().
- Applied gofmt.
Also:
- Build(mage): optionally include -a and/or -v during go build.
