Support for missing works_max

[osy]

Allow a package to not have to specify the max compatible version.

[Shugabuga]

Sorry it took me so long to review this PR. Just curious on why you did a few things:

1. Why did you remove the text "iOS" from the web template?
2. In DebianPackager.py, why did omit compatible_max if a user wants to provide their own tags?

[osy]

1. Because tweak_compatibility already has the word “iOS” so the web template shows up as “iOS iOS 11”
2. Because in my use case I had a compatible_min but no compatible_max and it threw an error. I changed it to make compatible_max optional.