Issue 16 & 29

Issue 16: initialize html with style="display:none".
- add 2 functions to show/hide elements by id (progress/khz/kbps/time)
- add functions to stop/play function

Issue 29: on press play try reset currentTime = 0 by using if statement.
I appreciate the clean up, but it's generally good practice to keep all the changes in a PR related to a single issue. It makes it much easier to do code review. Just for future reference.