Add com.snowplowanalytics.snowplow/application/jsonschema/1-0-0 (close #1418)

[matus-tomlein]

Add a schema for the application context entity tracked in Web and other apps that specifies the version number of the application. This can be in the form of semver or a Git commit SHA, so the schema doesn't put any further limits on it other than the max length.

Note that we already have a application context entity that is tracked on mobile – it has the vendor com.snowplowanalytics.mobile. In addition to the version, it also has a required build property that is available in mobile app builds. We can't reuse the same as the build number is not so useful on Web apps.