Add support for extending head block on dashboard

[jaxwilko]

By default, Block::put('key') & Block::endPut() defaults to overwriting instead of appending.

This change means calls to Block::append('head', $content) will function correctly for the dashboard.

[what-the-diff]

• The endPut() method was changed to accept a boolean parameter.
• If the value of this parameter is true, then it will render the block immediately instead of waiting for all blocks to be rendered at once in Block::end().

[jaxwilko]

• The endPut() method was changed to accept a boolean parameter.
• If the value of this parameter is true, then it will render the block immediately instead of waiting for all blocks to be rendered at once in Block::end().

Bad bot