* Moved attachaments POST url from /issues/attachments to /attachments
* Implemented attachment upload on release page
* Implemented downloading attachments on the release page
* Added zip and gzip files to default allowed attachments
* Implemented uploading attachments on edit release
* Renamed UploadIssueAttachment to UploadAttachment
This commit improves templates readability, since all of them use consistent
indent with all template command blocks indented too.
1. Indents both HTML containers such as <div>, <p> and Go HTML template blocks
such as {{if}} {{with}}
2. Cleans all trailing white-space
3. Adds trailing last line-break to each file
