Replace 'magic strings' with enums

[Jericho]

Replace string parameters that expect a value from a pre-determined list to enums. For example, when retrieving a list of clients, you can set a filter criteria on the status field which can one of the following 5 values: 'all, 'pending', 'trial', 'active' or 'suspended_all'.

I have identified the following parameters:

• GetCampaigns: status, sortBy, sortDirection
• GetCampaignsCount: status
• GetClients: status, sortBy, sortDirection
• GetClientsCount: status
• UpdateClient: status
• GetLists: sortBy, sortDirection
• UpdateList: status
• AddListField: fieldType
• GetListMembers: status, sortBy, sortDirection
• GetListMembersCount: status
• GetListLogs: logType
• GetListLogsCount: logType
• CreateMailing: type, encoding, transferEncoding
• GetMailings: status, type, sortBy, sortDirection
• GetMailingsCount: status, type
• UpdateMailing: type, encoding, transferEncoding
• GetMailingLogs: logType
• GetMailingLogsCount: logType
• SendRelay: encoding
• GetRelayLogs: logType
• CreateTrigger: encoding, transferEncoding
• UpdateTrigger: encoding, transferEncoding
• GetTriggers: status
• GetTriggersCount: status
• GetTriggerLogs: logType
• GetTriggerLogsCount: logType
• UpdateUser: status