Custom widget should be renamed

[peter-yanase]

I think the name "custom widget" is slightly confusing. I suggest renaming it to "custom html."

That way it would be more obvious that:

• The Pomodoro timer is a sample html code including an iframe.
• The user will need to write both HTML and CSS to alter it.
• The user can include anything there, ranging from simple images and text to multiple iframes.