Make "boost5" value user configurable

[otzbergnet]

Some users might consider the limit of 5 too small and would thus prefer to be able to set their own value.

@gingerbeardman suggested that some users might want to have this on all the time

[otzbergnet]

Initial Thought:

Allowing users to set their own number of requests to boosts seems a reasonable choice. I am thinking of a dropdown in the extension settings getting as high as 50.

I am very hesitant about making this an "always on" function for two reasons:

• I would like to be respectful to the archive.org API avoiding unnecessary calls
• I would like to avoid for this extension to inadvertently help collect an entire usage profile of a given user

[gingerbeardman]

I think this feature is a bit of pandora's box

[otzbergnet]

This feature should be available with the next release of Wayback - it will have a drop down in the settings screen, which will allow users to select from 5, 10, 15, 20, 30, 40 & 50

[otzbergnet]

#45 includes this