Ensure x values added in incrementing order in TlmGrapher

[ryanatball]

Here is a possible implementation that sorts the x values if one with a lower value is attempted to be inserted.

if x_values.length ==0
x_values << x_value
y_values << y_value + @y_offset
else
if x_values.last <= x_value
x_values << x_value
y_values << y_value + @y_offset
else
loc = x_values.bsearch_index{|x| x > x_value}
x_values.insert(loc,x_value)
y_values.insert(loc,y_value +@y_offset)
end
end
@plot.redraw_needed = true