Branch product for older platform versions

[justint]

Since this plug-in's v0.4 release, major platform version compatibility issues have come up with versions prior to 191.* (2019.1). There's a notable quantity & variety of issues (new interfaces/classes/methods aren't available in older platform versions, migration to Java 11 in 203) that justify branching this product for older versions of the platform.

I've created a new branch 191.8026.42 to target the latest platform version with compatibility issues (2019.1). This branch will be built using an earlier version of Java and should be maintained with the intention of supporting all pre-2019.2 versions (for now, until I find more compatibility issues between versions below 191 that warrant another branching).

I've delayed the release of v0.4 until I can get both >2019.1 (master) and <2019.1 (191.8026.42) versions of the plugin functionally identical and stable.

[justint]

Fixed with the latest release(s): v0.4 & v0.4-2019.1: https://plugins.jetbrains.com/plugin/12407-usd/versions