Show plot history

[renkun-ken]

What problem did you solve?

Closes #171

This PR:

• Preserves historic plots in {tempdir}/images by updating the history plot file on plot.new and grid.new hook.
• Adds a command Show Plot History to show a WebView of historic plots.
• Fotorama is used in the WebView to present the plot history that provides thumbnails of images and allows user to navigate via click and arrow keys.

Known limitation:

• Currently, we replay plot on task callback, i.e. top level of user input. If user uses par(mfrow = c(a, b)) and produces multi-page images in a single callback (i.e. create plots of more than a*b so the page is cleared and a new page is created), only the last page can be replayed.
• If user uses par(mfrow = c(a, b)), when user adds a plot to the current page, it will be regarded as a new plot and saved to a new history plot file since I don't know a way to know if a page is flushed. For example, for par(mfrow = c(1, 2)), and user runs plot(rnorm(100)) twice, two plots files are preserved as history plots, unless user produces two plots in a single callback.

(If you have)Screenshot