OE0-18: Replace internal FHIR model with fhir.resources library

[sniedzielski]

Ticket: https://openimis.atlassian.net/browse/OE0-18

Required fixes after developing this ticket (detected errors during development after connecting models from 'fhir.resources' repository)

• Organization - https://openimis.atlassian.net/browse/OE0-23 - location and address, bank_account
• Group - https://openimis.atlassian.net/browse/OE0-23 - location and address
• :Contract - https://openimis.atlassian.net/browse/OE0-22

[lgtm-com]

This pull request introduces 25 alerts and fixes 10 when merging e7e31a7 into b9f16b6 - view on LGTM.com

new alerts:

• 9 for Module imports itself
• 9 for Variable defined multiple times
• 5 for Unused local variable
• 2 for Unused import

fixed alerts:

• 8 for Unused import
• 1 for `__eq__` not overridden when adding attributes
• 1 for Unused local variable

[lgtm-com]

This pull request introduces 33 alerts and fixes 16 when merging 65bc04e into b9f16b6 - view on LGTM.com

new alerts:

• 10 for Unused import
• 9 for Module imports itself
• 9 for Variable defined multiple times
• 5 for Unused local variable

fixed alerts:

• 14 for Unused import
• 1 for `__eq__` not overridden when adding attributes
• 1 for Unused local variable