Portal Metrics css / content enhancements

[rushirajnenuji]

• [x] Add padding to the left and right of the page
• [x] StatsView wording should be dynamic so it makes sense for the context – e.g. “this dataset” and “this repository” should say “this portal” when viewed in a portal. “Summary of holdings” heading can probably just say “Summary”

[rushirajnenuji]

Both the above CSS enhancements linked above are completed in the commit: https://github.com/NCEAS/metacatui/commit/8dc26d00b7840fd5e819106a1266c154dd83f876