refactor database schema upgrade to support skipping versions

[elrido]

This PR addresses a discussion in #1334.

Changes

• allow skipping versions for automatic database upgrades, by using version_compare smaller-or-equal checks to match all versions up to the comparison point.

Other considerations

• arguably, if-conditions are more readable and/or less error prone to switch-case-statements
• while the version checks are a little less performant, this should not cause much impact as the function only gets called if the current database version is below the current installed applications, so only once after each upgrade - this is not in a hot loop