Disable accounts select if the accounts list is empty [Tiny improvement at the UI]

[leonardodimarchi]

Disabling the accounts select if the accounts list is empty.

• Tested the change by updating the store to check if the select only disables if there is no accounts at the accounts list.
• The accounts placeholder doesn't show up, i'll take a look on that later on (should i create an issue on these little improvements?)
• I'm currently running only the frontend, cause i'm still digging on the API code to discover a way to run it

This is my first contribution at an open source project, i'll appreciate any tips or good practices for contributing here =)

Before:

After:

[punmechanic]

Looks good to me!