Travis: Simplify secret key management and create top level settings.
Travis: Simplify secret key management and create top level settings.

Introduce option to override settings from travis private variables set
in the travis interface which allows to modify build properties without
commiting modifications to the travis file.

Move all secret keys to be stored in travis private variables.

Fix YAML styling.

pasinskim/deployments,pasinskim/deployments,pasinskim/deployments,pasinskim/deployments