You have copied LastPass, however LastPass isn't a good design to copy. Passwords and sensitive info isn't only for "Sites". You also have Wifi networks, routers, credit cards, etc, not to mention many people need custom fields, like for Apple's stupid secret questions, or for recovery codes, etc. You've also taken the name Site too literally. Throwing an error if the URL is empty is a mistake. Don't assume the user doesn't know what he's doing and I doubt this app needs URLs to function.
I never liked LastPass because it's rigid on how you can store data. Surely username+password+ website is common enough, but give the user the opportunity to add custom fields. This is how KeePass and 1Password work, it's a proved design ;-)
On Android, when using the password generator on editing a new site, in order to complete the process I had to copy/paste the new password. This is bad, on Android at least, as the clipboard on Android is public and any app can register a listener for clipboard events. And again, on viewing the password, it got truncated, so the user is forced to copy/paste it.
I'm also uneasy about having my data uploaded to your servers. I realize data is encrypted before that, but given this is supposed to be open source, it would have been better if the apps were able to work offline or with Dropbox, then add the server stuff as an add-on.