Support more PowerShell file extensions

[Florian Feldhaus]

Currently IntelliJ IDEA by default only recognizes .ps1 as PowerShell files. Add at least PowersShell Module files .psm1. Consider recognizing the more specialized files as listed in this Blog Post https://richardspowershellblog.wordpress.com/2017/10/30/powershell-file-extensions/.

[Friedrich von Never]

The current plugin version supports .ps1, .psm1 and .psd1. As I can see, others are either XML variations or are tricky to support (and rarely used). For now, I consider this request done, but feel free to open new requests for particular file types on GitHub.

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