Added content to Qt SQL
Added content to Qt SQL

- more info on using SQLite
- how to access MySQL
- main classes of Qt SQL
- Added link to Qt SQL
- 2 punctuation issues (inserted commas)
- replaced "SQL module module" by "SQL module".
- one space after period instead of two
- limited lines to 80 positions
- added further explanations on QtSqlTableModel
  and QtSqlRelationalTableModel
- fixed problem with trailing whitespace

Edits in SQL section according to remarks by reviewers

Restored original format in License section (2 spaces after period).
Change-Id: I138ef32146b343b1fc745da3c5c85f8e056be025
Reviewed-by: Jerome Pasion <c10995d24f6b454503389e8d00d837aef038985d@digia.com>

kobolabs/qtdoc,kobolabs/qtdoc,kobolabs/qtdoc,kobolabs/qtdoc