algebra_by: Update Activity.qml

Remove commented code.
Use ReadyButton.qml instead of creating a component here.
Fix balloon expiring.
algebra_by: Update activity.js file

Move questionsLeft() function from Activity.qml to activity.js
Remove some unnecessary variables.
Fix scoring mechanism
core: Update Balloon.qml

Fix display of bad bonus when balloon animation completes. To do this,
use onStopped signal but detct it ONLY when balloon completes a loop of
animation and not when balloon is restarted.
core: NumPad.qml

Remove commented code.
core: Add new Score.qml file

Add the Score.qml file in core. The file has been taken verbatim from
petitlapin's github account.

Remove default anchoring from Score.qml, so that anchoring may be
enabled while using this element.
Bold the text and make it bigger and consistent with text size in
ReadyButton.qml
core: Add new file ReadyButton.qml

Create the Ready button element that contains the text "I am Ready!" and
add it to core. File gives a signal when the box is clicked.
core: Update core.pri with additions of new files

Add the new files ReadyButton.qml and Score.qml to core.pri