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.
Why are these two lines duplicated in both the `if` and the `else`? Can we move them outside the `if` statement?