'source' property to specifiy source for values and passwords

[mlookaxw]

As Is

For field values there are separate properties ("property" and "value") to configure the field value.

For certificates password there are separate properties ("password" and "password-property") to configure the password for a p12 certificate.

To Be

The source of the field values will be identified by a "source" property. This defines the kind of the "value" property. In case of "source" is equal to "value" the field value is directly configured by the value of the "value" property. In case of "source" is equal to "property" the field value is retrieved from the property named by the "value" property.

The source field for certificate passwords will be identified by a "source" property. This defines the kind of the "password" property. In case of "source" is equal to "password" the password is directly configured by the value of the "password" property. In case of "property" the password is retrieved from the property named by the "password" property.

The older formats of the configuration file will be converted automatically into the new format.

Background

This enables a better extensibility of further sources (e.g. environment variables, see issue #29).
Also is makes it easier to search for not configured values or passwords (just search for "value": null or "password": null).