[Merge] lp:~tiagosh/dialer-app/refactor-ussd into lp:dialer-app

[Gustavo Pichorim Boiko]

Review: Approve

Did you perform an exploratory manual test run of the code change and any related functionality on device or emulator?
Yes

Did CI run pass? If not, please explain why.
No, but that's because changes in telephony-service are needed

Have you checked that submitter has accurately filled out the submitter checklist and has taken no shortcut?
Yes

Code looks good and works as expected!
-- 
https://code.launchpad.net/~tiagosh/dialer-app/refactor-ussd/+merge/256943
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