If a layer is interactively installed by visiting a file the progress
file is updated without being properly initialized before causing a
division by zero.
Now `spacemacs/update-progress-bar` will ignore the call if
`spacemacs-loading-dots-chunk-threshold` is <= 0.
Spacemacs is slow to startup so better give it a not buggy progress bar :-)
* Move progress bar code to core-progress-bar.el file
* Remove the counters at the end of the progress bar
* Fix update of the progress bar value
* Fix progress bar size when staring Emacs maximized
