Iwehrman/rework code hint manager

[iwehrman]

Implements the revised code hinting API as described at https://github.com/adobe/brackets/wiki/New-Code-Hinting-API-Proposal. Along with the previous commits, this directly addresses #1624 and #2258. The API should be flexible enough to allow a solution to #2286 as well.

cc @joelrbrandt @RaymondLim

[redmunds]

The hintProviders object members (indexes?) are modes, so I think this code would be more clear if "providerName" was changed to "modeName".

[redmunds]

First, you need to check to see if anything is selected. If nothing is selected, then return. Otherwise, event.preventDefault() will be called (below) and the Return or Tab will not get inserted into the page.

[iwehrman]

With the updated rotation logic, if nothing is selected then up/down navigation will always cause something to be selected. If the user presses tab/enter and nothing is selected, the default handler won't be prevented because the final else-if branch won't be entered and instead the final if-branch will return before the prevention.

[redmunds]

Done with initial code review.

[redmunds]

This logic can be simplified:

        if (_inSession(editor)) {
            _updateHintList();
        } else {
            if (lastChar) {
                _beginSession(editor);
            }
        }

[iwehrman]

Yep! Fixed.

[redmunds]

Looks great. Merging. Thanks, Ian!