Improved update availability check

[Pidgeot]

Currently, an update is considered available if the online version string is not equal to the local version string. This has caused various annoyances for my beta packs which are hosted at a different URL but still check for stable updates.

I propose to add an additional two criteria, and a config setting to choose which to use. The default if not configured would depend on the file host.

• String equality. Currently the only option. Remains default for JSON and regex updaters.

• Lexical ordering, split on ., attempting conversion of parts to integers (basically semver).

• Timestamp comparison. Only available for DFFD, but preferred (default) in that case. If update timestamp is after the time of first launch for the local pack (saved to file), an update is available. Ideally include a delay and variance setting for staged rollout.

[Issue created by PeridexisErrant: 2017-03-13]