Update Brackets Sidebar Flex CSS

[puzzledShark]

Presently brackets is using an outdated version of flex, due to this the sidebar is not rendered properly within firefox

Firefox	Chrome

To fix this I have updated the box css that were here: https://github.com/adobe/brackets/blob/master/src/styles/brackets_mixins.less#L24-L69

with: https://github.com/KeniMorri/brackets/blob/boxFlexUpdate/src/styles/brackets_mixins.less#L24-L68

One error that arose due to this change is that the extensions dialog looked broken:

To alleviate this a few changes were needed, I changed the css to use .vbox, and removed the <br/> that was present in the html to fix this issue.

The proposed changes can be viewed in the comparison below: https://github.com/adobe/brackets/compare/master...KeniMorri:boxFlexUpdate

[K-LV]

I can also confirm that, after adding this patch, the context menu is now visible when right-clicking in Firefox. However, it goes away unless right-click, hold, and hover over the menu.

[puzzledShark]

Although in general, the fixes I proposed in PR #182 does correct the issues in firefox, in relation to these lines: https://github.com/humphd/brackets/blob/bramble/src/styles/brackets_mixins.less#L71-L76 I cannot seem to find a suitable replacement for them within the flex method. I can't find anything in relation to it breaking yet though.

[humphd]

What about elsewhere in the CSS/LESS? Are there other places that need similar fixes?

[puzzledShark]

Updated main post