Label formatting: move global styles away from label template

[arbolitoloco]

Historically there are some design choices made directly in collections/reports/labeldynamic.php that affect the printed labels and are controlled by different parts of the label format editor.

Specifically talking about the styles used for :

• .row (uses flexbox, which might not be the ideal way to position things, since it's responsive and we might want to be more strict about layouts);
• .label (uses width percentage based on proportion selected by number of columns in label format editor, which might prevent users from easily adjusting very specific label fixed sizes);
• .label-header and .label-footer (use clear methods that might result in weird overlapping depending on other choices)

Ideally we would be able to move these choices from the page itself to either global, custom, or label-specific styles, so that users can have easier control over design. To do that, the label editor and related classes, as well as default formats and styles will have to be adjusted as to not create problems for existing portals.