Activate FlowIDE when `all` is true

Hi!

Currently I'm working on a project that has set `all=true` in `.flowconfig` file, so there's no `// @flow` in any of the files and as such FlowIDE does not activate at all.

I believe that if `.flowconfig` exists, FlowIDE should check if `all` option is present and all features should be activated just like when file has `// @flow` on top