Remove the custom request util

Since it wasn't the cause of the memory leak, it'd cause unnecessary
maintenance to still include it.
Update booru to not use the custom request util
Removing usage of util.js from plugins/rehost.js
Also doing some minor changes for better error handling and reporting.
Merge pull request #25 from HigherFive/rehost-fix

Removing usage of util.js from plugins/rehost.js
Merge pull request #26 from Sebmaster/remove-request-util

Remove request util