Doc: Work on iOS platform notes

Change-Id: I0e70937d2ee32f2e1868da1ac0d67e9b494d17d5
Reviewed-by: Jerome Pasion <jerome.pasion@digia.com>
Reviewed-by: Topi Reiniö <topi.reinio@digia.com>
Doc: Reorganized information in smaller topics

The getting started page had grown bigger so it was necessary
to break it up into smaller chunks for easier maintenance in
the future.

Besides reorganizing existing information, added a section about
publishing to Google Play, and fixed a few language and linking
issues.

Task-number: QTBUG-33580
Change-Id: Ic84dfb171b09c394e0bde977e7909b234e82775f
Reviewed-by: Eskil Abrahamsen Blomfeldt <eskil.abrahamsen-blomfeldt@digia.com>
Reviewed-by: Jerome Pasion <jerome.pasion@digia.com>
Reviewed-by: Leena Miettinen <riitta-leena.miettinen@digia.com>
Doc: Added information about the Try Qt Enterprise page.

Task-number: QTBUG-33360
Change-Id: I2e7e3e8f9256a52ffe8f3fabe0238413cc7a3f8a
Reviewed-by: Leena Miettinen <riitta-leena.miettinen@digia.com>
Reviewed-by: Topi Reiniö <topi.reinio@digia.com>