Use a lightweight docker image to replace fragile jq, shasum, etc, fixes #100, for #46, fixes #96, fixes #93

[rfay]

• shasum is also required and must be handled #100
• [docs] README should explain that ddev get is when config translation happens, and you need to repeat if changing Platform config #96
• Add-on shouldn't use jq, base64, perl, etc without some notice or requirement #46
• Homebrew base64 does not support base64 -w #93

We've been very fragile with regard to requiring the user to install

• base64
• jq
• perl
• sed
• shasum

This switches to using a lightweight docker image to do those activities.

[gilzow]

I dont know... jq is kind of a beast. 😄

[rfay]

It's just using jq in a lightweight container, so we don't have to worry about 1000 varieties of it.