[BUGFIX] CSS: Default vertical spacing for blocks

Forms, tables, texts need a clear structure and obvious
visual distinction. Our Backend currently does not
deliver strong defaults for extensions.

Many modules already work around this lack of structure
by adding extra spacing and horizontal rules:

- DocumentTemplate::spacer(x-Pixel)
- DocumentTemplate::divider()

This patch brings vertical spacing based on CSS for:

- p
- ul / ol
- dl
- blockquote

Change-Id: I93a1a43b21d6e56db822558c6d4be0103097ed98
Resolves: #48540
Releases: 6.2
[TASK] Remove styles for former ExtensionManager

Deleted CSS files that bring styles for former EXT: em.

Change-Id: Ia8bd3c8971ba5aabb7792a08b4cff577d1f95ec6
Resolves: #48550
Releases: 6.2
[TASK] Clean-up and update INSTALL.txt

- Update copyright year
- Includes required module "fileinto" in recommended section
- Adds reference to recommended library FreeType 2
- Corrects typo3.org deep links accordingly (T3O)

Change-Id: I067b2d930c1a6ffa15ea61f10723e29eb434f491
Resolves: #48541
Releases: 6.2