Ews ghana initial integration

We have two domains: tanzania and ghana and for these two domains logic is similar but models are slightly different. Look at this lines: https://github.com/lwyszomi/commcare-hq/commit/72c48d729473d9facd55ddae0459874dd1e82c87#diff-1dfdbdf49c0f631cf0895569f668fba2R111. Thanks to this we can use methods from ILSGatewayEndpoint also in GhanaEndpoint.