Add ASCII charts

[afazio]

Allow the user to hit <spacebar> to toggle a cursor that can be moved with the <up> and <down> keys. When a security is selected, show a historical ASCII chart for that security. Can use gnuplot for nice axis rendering, or can use an extended, multiline sparkline concept that uses the unicode symbols from pysparkline, allowing the user to configure how many lines to use for charts. Allow user to use <right> and <left> keys to adjust chart to predefined time ranges.