Improvements to PluginManager plugin

[JohnTheGr8]

The main change introduced here is the use of conditional http requests when fetching the plugin manifest json. This allows us to always check for changes to the manifest repo when running one of pm install, pm update, with very little performance overhead (for me it is about 50ms). It also allows us to simplify the relevant code a bit.

Also some quick refactoring in PluginsManager and a couple quality-of-life enhancements:

1. typing pm inst and hitting tab would autocomplete to pm install without a space at the end (same for the other base commands)
2. fix incorrect link (for some plugins) when selecting to open an issue from the context menu

PS: I missed #682 until I started writing this PR text... my apologies. I see similarities, perhaps we can pick some of the missing changes into this PR?

[taooceros]

Should we expand the helper class instead of creating a new httpclient for plugins manager only? Also this may not follow the proxy setting.

[JohnTheGr8]

Should we expand the helper class instead of creating a new httpclient for plugins manager only? Also this may not follow the proxy setting.

Yup, you're right, I wanted to keep it simple but I forgot about proxy settings... Will add a helper method inside Http that accepts a HttpRequestMessage

[JohnTheGr8]

There's one issue I just noticed: launching Flow and opening Settings > Plugin Store (without first using pm install/update) will show no plugins...

Possible workarounds:

1. actually fetch the plugin data in PluginsManager's InitAsync (which will add a few ms to the init time)
2. call PluginsManifest.UpdateManifestAsync() when the user opens settings (or something similar)

thoughts?

[taooceros]

I would consider that we just call download manifest in init? We can decide not to await that so it won't change init time.

[JohnTheGr8]

I would consider that we just call download manifest in init? We can decide not to await that so it won't change init time.

Alright, was hoping for this since I am not very familiar with WPF 😛 It's pretty fast with the CDN link, anyways...

[taooceros]

I would consider that we just call download manifest in init? We can decide not to await that so it won't change init time.

Alright, was hoping for this since I am not very familiar with WPF 😛 It's pretty fast with the CDN link, anyways...

lol it's not related to WPF. Flow waits for plugin init before showing up.

[JohnTheGr8]

I would consider that we just call download manifest in init? We can decide not to await that so it won't change init time.

Alright, was hoping for this since I am not very familiar with WPF 😛 It's pretty fast with the CDN link, anyways...

lol it's not related to WPF. Flow waits for plugin init before showing up.

I meant my other solution, the second one ;)