Some proposed improvements

[vjr]

Following proposed changes:

• Swap network upload/download indicators (system chart already is this way). People typically prefer to see the downloads more than uploads?
• Add a "use bits" preference to show network bandwidth in bits-per-second instead of bytes.
• Add custom bandwidth format string util method.
• Show sub-GHz CPU frequency as MHz instead of always GHz.
• Increase some indicator widths to prevent widgets jumping around when label texts change.

[danirabbit]

Please break this up into individual branches for unrelated changes. There's no way to merge this and keep a reasonable commit history

[vjr]

Converting to draft while I work on separate PRs.

[vjr]

Discarding this PR in favour of the following four separate PRs:

#540 #541 #542 #543