refactors client lib and relay-checker

client/lib.go

pluginmgr/webapi/plugins.go

plugins/webapi/broadcastData/plugin.go

plugins/webapi/findMessageById/plugin.go

plugins/webapi/findTransactionHashes/plugin.go

plugins/webapi/getTransactionObjectsByHash/plugin.go

plugins/webapi/getTransactionTrytesByHash/plugin.go

tools/relay-checker/config.go

tools/relay-checker/config.json

tools/relay-checker/main.go

tools/relay-checker/parameters.go