Upload form redesign and upload button visibility

[akhil-rana]

1. The Slide Upload form is slightly redesigned to match the application.
2. Now, the upload button will only be visible to the user who has the permission to upload a slide.(Using what can i do route)

Old:

New:

[birm]

Hm, it looks like this removed the ability to add multiple slides at once.
I have no objection to that, but in that case, we can probably simplify the code to only have to deal with one slide at a time.

[akhil-rana]

I also noticed that the multiple keyword was missing in the previous design itself.
I realised that,
It was removed in #313

[birm]

Ok, then we can merge this and let simplifying the code be a separate issue.