Implement label-width-and-position mode for list layout

Remove the partial handling of list indentation and implement the default
option for list-level-position-and-space-mode.

http://docs.oasis-open.org/office/v1.2/os/OpenDocument-v1.2-os-part1.html#property-text_list-level-position-and-space-mode
Implement label-alignment mode for list layout

Add handling for the label-alignment list style element. This commit does
not implement the text:label-followed-by attribute so for now a hard coded
padding has been substituted

http://docs.oasis-open.org/office/v1.2/os/OpenDocument-v1.2-os-part1.html#__RefHeading__1416522_253892949
Initialise indents and widths to default values

This prevents us from being unable to sum these values together
Remove redundant variables and add further comments
Added some layout tests for list styles

Added one test for label-alignment styling and another test for
label-width-and-position mode