[#144] handle otpauth URLs with server port numbers

[runejuhl]

This fixes pass-otp not being able to handle OTP URL with a HTTP port numbers embedded, by slightly rewriting the regex used for taking the OTP URL apart.

URLs with port numbers would otherwise cause errors like the following:

Cannot parse OTP key URI:
otpauth://totp/some.domain.com:username@some.domain.com:443?secret=ABCDEF

[KlavsKlavsen]

This would be REALLY nice to get merged

[tadfisher]

Unfortunately this breaks some test cases in insert.t, as the regex prevents parsing the account name in all cases. I've continued this in #158 which appears to solve the underlying issue.