refactor initialization

this decreases the chance of deadlocks on startup
it should also decrease the startup time.
[#56592122]
[#56615394]
applet calls javascript when it is ready

This fixes an issue with FireFox on OS X and some versions of
Java 7. It is also a more efficient way checking if the applet
is ready. And finally it might also reduce the blocking of the
JS thread because it won't be trying to call into Java so much.

[#56872730]
use the signed jar instead bare class

this removes the warning about running unsigned code

[#56994066]
Don't reference applet too early

see: http://concord-consortium.github.io/applet-tests/timing/
also this changes to the call to remove to dig into an
issue with IE reloading the applet when it is removed

[#56872730][#56994202]
use IE safe applet removal approach

http://concord-consortium.github.io/applet-tests/removal-of-tag/
[#56994202]
fix formatting
First pass at handling IE multi threading behavior

[#57114958]
merge vernier-sensor-applet into sensor-applet

if we create a pasco sensor applet it will have the same
interface as the vernier-sensor-applet, so the abstraction
is unnecessary

[#57181910]
document sensor-applet API methods

[#57200194]
move sensor-applet to top-level, preparing for standalone

[#57200194]
remove dependency on lab.config

[#57200194]
remove duplicate measurementType

[#57200194]
move units-definition to sensor-applet

this is useful for code using the sensor-applet outside of lab
[#57200194]
add precision to sensor-definitions

this isn't currently used by the sensor model, but it will
be used by the old inquiry-space-importer and probably 
will be used by the sensor model soon.
[#57200194]
sensor-applet embedder says where to add test applet

this is useful so the test applet can be centered within
a certain part of the page. this is not used by the 
sensor model, but will be used externally and could
be useful to sensor model.

[#57200194]