IE11 not working with 1.15.0+

[cmdcolin]

Visiting http://jbrowse.org/code/JBrowse-1.15.0 does not work in IE11 and gives an error which is basically due to async/await being used in the code

[cmdcolin]

This should be fixed on dev now after some somewhat crazy switching of dependencies. There was possibly something in babel like _Object$defineProperty that could have been an alternative but otherwise this works now