Add Contribution Page settings for Review and Make Contribution button text

Contribution Pages can be important to some organizations who do a lot of fundraising. It would be nice if the buttons were customizable, so they could say 'Donate', 'Give', 'Get Membership' or whatever the user might want.

Proposal: Add two fields to Contribution Pages: review_button_text and submit_button_text. These settings could live on the main settings tab, underneath "Use a confirmation page?" with review_button_text hidden and shown conditionally. If these are populated, use these values, if not, fall back to the default (Contribute or Review your contribution followed by Make Contribution).