VizBlocks: Draw a bar chart

[tanhengyeow]

This issue keeps track of work that allows users to draw a bar chart plot via blocks we offer. To draw a line graph, we need blocks that can:

• [x] Draw x/y axis
• [x] Read x/y values from user
• [x] Map x/y values to x/y axis
• [x] Draw a bar on the x-axis (reference value from y-axis)