Add theme button on headbar in slide-editor page

[honglio]

Theme button is a drop-down button of 9 theme option. When user choose one theme, it add several textbox with pre-defined font color, size, margin, line-height in operating table, and the background-color also changed to pre-defined color. Theme button should right before background button. e.g.

[honglio]

We could add a tourtorial to tell user that you could use copy and paste the slide snapshot on left sidebar, in order to simulate theme.