changes for new download webpage

This MR is in response to !201 (merged)

Fixes the issues i could quickly find going top to bottom from the page. These are also tested on mobile version, no major out-of-place artifacts were found

Changes:

1. center aligns the top logo and text.
2. makes the main download box look better.
3. adds a tasteful light lavenderish shadow to the main download box to match the overall theme of the page.
4. makes the donate button default call to action, makes it visible above-the-fold for better response.
5. moves the need-help section to near the footer of the page.

screens:-