[$10] - Footer margins

[birdofpreyru]

On the pages served by the code from this repo, margins around the footer are too large (the screenshot is from the Dashboard page for past challenges in Code track, but similar problem is with all pages):

We should decrease the spacing (1) to a reasonable size, and replace spacing (2) by padding (i.e. it will be to have that spacing there, but it should be a part of the footer, thus dark gray). Please have a look at the current challenge listing page, we want to have the footer looking similarly to that page.

Also, please check that changing these does not break the infinite scrolling of past challenges (for the reference, here are the ticket and PR implementing that infinite scrolling: #906, #962. If you check my last comment in the ticket, at the moment the logic behind when we trigger the loading of new porting of challenges relies on a hard-coded height of the footer. Probably, you will have to tune corresponding constant after you change margins around the footer)