Add support for Vortex Collection downloads

[Curtiss02]

Not sure if this is entirely withing the scope for this project, but I updated it for myself anyway so I figured I might as well do a PR. I've added an additional image to the templates folder that corresponds to the download button on the Vortex that you have to click manually when using a free account. When clicked this brings up the nexus download window, and when the download starts it will bring the Vortex window back up, allowing you to just start the app and walk off while it downloads all the mods.

Haven't done too much testing but was able to download a 100+ mod collection on my PC with no issues.

[parsiad]

Thanks! Just some small nits.

• Change templates/3_30_vortex-dl.png to templates/3_30_vortex_download.png
• Change assets/vortex-dl.png to to assets/vortex_download_page.jpg (note the JPG)
• Only modify the README as below (i.e., do not add dependencies or extra text)

-Specifically, while Nexus AutoDL is running, any time a [mod download page](https://raw.githubusercontent.com/parsiad/nexus-autodl/master/assets/mod_download_page.jpg) is visible on your screen, Nexus AutoDL will attempt to click the download button.
+Specifically, while Nexus AutoDL is running, any time a [mod](https://raw.githubusercontent.com/parsiad/nexus-autodl/master/assets/mod_download_page.jpg) or [collection](https://raw.githubusercontent.com/parsiad/nexus-autodl/master/assets/collection_download_page.jpg) download page is visible on your screen, Nexus AutoDL will attempt to click the download button.

[Curtiss02]

I have adressed the nits in the previous comment. Let me know if any further changes required. Thanks :)

[mirko8054]

Hello, i have to bump this conversation. Vortex GUI was updated and now the bot does not work, its unable to recognize the buttons