New dev/task to initialise DataObjects for existing datasets

[nathanbrauer]

New task is based on the original task built for SiteTree but is now extendable for any DataObject enabled with Fluent. To prevent duplicate code, the original task now extends the new task.

Included updated documentation

cc: @muskie9

[tractorcow]

Looks good but you have some linting issues to fix.

FILE: ...-fluent/silverstripe-fluent/src/Task/InitialDataObjectLocalisationTask.php
--------------------------------------------------------------------------------
FOUND 1 ERROR AFFECTING 1 LINE
--------------------------------------------------------------------------------
 284 | ERROR | [x] The closing brace for the class must go on the next line
     |       |     after the body
--------------------------------------------------------------------------------
PHPCBF CAN FIX THE 1 MARKED SNIFF VIOLATIONS AUTOMATICALLY
--------------------------------------------------------------------------------


FILE: ...stripe-fluent/silverstripe-fluent/src/Task/InitialPageLocalisationTask.php
--------------------------------------------------------------------------------
FOUND 1 ERROR AFFECTING 1 LINE
--------------------------------------------------------------------------------
 48 | ERROR | [x] The closing brace for the class must go on the next line
    |       |     after the body
--------------------------------------------------------------------------------
PHPCBF CAN FIX THE 1 MARKED SNIFF VIOLATIONS AUTOMATICALLY
--------------------------------------------------------------------------------

[tractorcow]

As commented

[nathanbrauer]

Just pushed the linting changes. I also discovered the minimum php for this branch is ^7.1, so I made a few adjustments to prevent fatal errors.