[ticket/10744] Prevent installing styles with reserved names

PHPBB3-10744
[ticket/10744] Type hint objects for IDE usages

PHPBB3-10744
[ticket/10744] Fix some doc blocks

PHPBB3-10744
Merge pull request #3094 from nickvergessen/ticket/10744

Ticket/10744 Prevent installing styles with reserved names
[ticket/10442] Adds <dd>&nbsp;</dd> to <dl> for xhtml correctness

PHPBB3-10442
Merge pull request #3164 from Crizz0/ticket/10442

[ticket/10442] Adds <dd>&nbsp;</dd> to <dl> for xhtml correctness
Merge branch 'develop-olympus' into develop-ascraeus