More default values and simplify onap config

More default values and simplify onap config

Populate more default values for ansible all.yml configuration
to make it simpler by default for user.

Removed project_configuration variable as it caused just
confusion. Replaced that mostly by using app_name variable.

According to above changed simplified actual configuration
config/application_configuration.yml used to install onap.
Mostly removed repeation of comments.

Also updated ansible/application/README.md that was not
updated for a while.

Issue-ID: OOM-1633

Change-Id: Idcc4c510b64bb61edd874d0e0616cdb41938f2d3
Signed-off-by: Samuli Silvius <s.silvius@partner.samsung.com>