Migrate the static fields in PidginAccountEditor to AdwEntryRow

I also moved the proxy port to an entry row instead of using a spin button. In
Pidgin 2 we just used an entry and used atoi() on it, so that's what I'm doing
here.

Testing Done:
Modified the alias and proxy settings and made sure they were saved properly.

Reviewed at https://reviews.imfreedom.org/r/1994/