Fixing some issues in section_case-studies-database.xml

* improved some wording
* replaced "SSL" by "SSL/TLS"
* changed Postgres to PostgreSQL
* removed "self-signed" while using certificates

Closes-Bug: #1342912

Change-Id: I45753743c9a88990b2d087ffbbddea6be6d2ff63
Merge "Fixing some issues in section_case-studies-database.xml"