Progress bar

[Cwpute]

To help with situations like i found myself in in issue #55 , i'd like the app to feature a progress bar in its UI so that you know how much of the process has been done, how much of it it still has to do, and if it is indeed progressing at all.

[flozz]

Hello,

Sadly it is not possible to implement a progress bar (Guetzli give no info about its progress when encoding a JPEG). I will implement later other choices for JPEG encoding that will be way faster and so the progress bar will be less useful anyway :)