Dropbox.Api 5.0.0

Change Notes: - Move officially supported versions to Net45 and NetStandard2.0 - Migrate from VS2015 to VS2017 build system - Move all build targets into single CSProj file - Add support for PKCE oauth flow - Add PKCE Oauth Example - Add System.Security.Cryptography as dependency (49cee186b12822462483dbca08dfb1335f55efbf) Files Namespace - Add internal_error to SearchError union. - Add locked to LookupError union. - Add cant_move_into_vault to RelocationError union. - Add MoveIntoVaultError union. - Add SearchMatchFieldOptions struct. - Add optional match_field_options to SearchV2Arg struct. - Doc/example changes. Sharing Namespace - Add is_vault to SharePathError union. - Add invalid_shared_folder to AddFolderMemberError union. Team Namespace - Make members field of LegalHoldsPolicyUpdateArg struct optional. - Add app_folder_removal_not_supported to RevokeLinkedAppError union. - Doc/example changes. Team Log Namespace - Add auto_approve to InviteMethod union. - Add moved_from_another_team to InviteMethod union. - Add moved_from_another_team to MemberStatus union. - Add no_one to SharedLinkVisibility union. - Add optional new_team to MemberChangeStatusDetails struct. - Add optional previous_team to MemberChangeStatusDetails struct. - Add external_sharing_create_report_details to EventDetails union. - Add external_sharing_report_failed to EventDetails union. - Add content_administration_policy_changed_details to EventDetails union. - Add external_sharing_create_report to EventType union. - Add external_sharing_report_failed to EventType union. - Add content_administration_policy_changed to EventType union. - Add send_for_signature_policy_changed_details to EventDetails union. - Add external_sharing_create_report to EventTypeArgs union. - Add external_sharing_report_failed to EventTypeArgs union. - Add content_administration_policy_changed to EventTypeArgs union. - Add send_for_signature_policy_changed to EventTypeArgs union. - Add SendForSignaturePolicy union. - Add ExternalSharingCreateReportDetails struct. - Add ExternalSharingReportFailedDetails struct. - Add ContentAdministrationPolicyChangedDetails struct. - Add SendForSignaturePolicyChangedDetails struct. - Add ExternalSharingCreateReportType struct. - Add ExternalSharingReportFailedType struct. - Add ContentAdministrationPolicyChangedType struct. - Add SendForSignaturePolicyChangedType struct.