"f" for "Forward" collides with "Change files" binding

[mjs]

Also fixed doubled up label for history bindings ("Back" was used twice).

[mjs]

I chose some bindings that made sense to me but I'm open to other ideas.

[coveralls]

Coverage remained the same at 83.362% when pulling 72f1f40 on mjs:fix-history-bindings into e19c06f on dajva:master.

[dajva]

Oh, how did I miss that. Thanks for fixing it. :)

Some comments:

1. Still want the labels to be "Back" and "Forward" since that is the terminology that is used throughout the package.
2. Regarding the bindings, I think we can keep 'b' since that is not taken. I would suggest using 'w' for forward since that may give some kind of mnemonic with 'w' in forward and is also on the left hand to ease the combination with the 'm' menu key. For evil users it's also a familiar binding for moving forward.

[mjs]

Done!

[dajva]

Thanks a lot!