[MAINT] Rename table header titles

[nathanbaleeta]

This PR renames the website registry table header titles as follows:

• License to Open license
• Past year of activity to Activity

[nathanfletcher]

@nathanbaleeta have you run it locally to see how the CSS would look like?

[nathanbaleeta]

@nathanbaleeta have you run it locally to see how the CSS would look like?

Good idea, thanks @nathanfletcher, I will iterate on how it goes.