Add actions to the Ranks admin screen

See #175
Add actions to the rank functions

See #175
Merge branch 'issue-175'
Add action below Text field of My Points widget

Allows for more instructions to be added regarding other placeholders,
for example.

See #179
Pass correct variables to actions

See #175
Add a function to format a rank for display

See #182
Add a function to format a user's rank for display

Includes unit tests.

See #182
Add `%ranks%` placeholder to the My Points widget

Includes unit tests.

Fixes #179
Merge branch 'issue-179'
Refresh language files

New strings introduced in #179