Redesign decryption UI

[kkuehlz]

• Import bootstrap into the iFrame
• Change text display from textarea to div
• Make links clickable (requires escaping input)
• Keep hidden textarea for copying text

This pull request closes #48.

Submitter Checklist

• [x] Tested on Firefox (npm run firefox)
• [x] Tested on Chromium (npm run chromium)

[kkuehlz]

@yvbbrjdr Can you please try again? The regex failed to compile in Firefox because lookbehinds are not yet supported. Should work now.

[yvbbrjdr]

@keur https://github.com/yvbbrjdr will be decrypted to https://github.com/;yvbbrjdr.

[kkuehlz]

@yvbbrjdr fixed and pushed