Add a history for each variable and a comment box about a variable in Runmanager

**Original report ([archived issue](https://labscript-suite.github.io/labscript-suite-bitbucket-archive/#!/labscript_suite/labscript/issues/24)) by Ian B. Spielman (Bitbucket: [Ian Spielman](https://bitbucket.org/%7Bbff0d3df-2ed5-4ff6-b13d-ce6cd935edb1%7D/), GitHub: [ispielma](https://github.com/ispielma)).**

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