ICS2: general readability improvements and inconsistency fixes #945

This issue is part of the ongoing work on general readability improvements and inconsistency fixes in ICS2.

Suggestions

• “an unbonding period of three weeks”: replace unbonding period with trusting period
• the difference between clientType and clientState is unclear, especially when it comes to the API defined
• “but they must expose this common set of query functions to the IBC handler.” is not follow by any set of functions
• in createClient why both abortTransactionUnless and abortSystemUnless?
• the difference between queryChainConsensusState, queryConsensusState, and getConsensusState (from ICS24) is unclear
• the difference between Chain queries and On-chain state queries is unclear
• it's not clear what the Implementation strategies are for

cc @crodriguezvega