Bug 1074732 - [Messages] Create a mixin to handle the select UI model

- Unbind the selected inputs logic from DOM tree structure. Create a selection module that listens to input select changed and return the selected data.
Previously I tried to put `checkInputs` ,  `toggleCheckedAll` and `cleanForm` into Selection module, but they got slightly difference here(threadUI need to update additional UI in `chooseMessage`, I'm thinking if there is a better way to avoid this). So currently I still keep the UI update task in panels. I think it's possible to moving all of the input selection related logic and UI into this module at first, but separating the data logic and UI updating to different place is also an idea(We still kept and UI update in panel and only update the visible input in container based on selected data). Wdyt?