Resolve "Bug with iframe during the email signing"

Closes #23 (closed)

@alexey.lunin @mikhail.dorokhovich please review. I wasn't be able catch this bug, but I refactored signEmail method which is a root cause, added more error handling here, so if this bug will appear again, it should give you more details.

added needs review label and removed DevInProgress label

Looks good to me

added reviewed label

added 1 deleted label

removed needs review label

added ReadyForMergeInMaster label

assigned to @gospodin.bodurov

merged

mentioned in commit 5fcfdd0b