fixed "scene" attribute of trigger

we want this.fn to be constructed below using fn
also removed dead code
ignoring null in replaceVariables()

seriously, it is too commonly used to trigger an error
<restart/> was so broken...

Added getFirstScene() to interpreter not to look for first label each
time.
Shifted the stack before changing the scene so that <restart/> inside
<sub> or <trigger> does not make stack grow.
Added a small extension that dumps the stack to 'backtrace' variable.
wse build updated

nothing to see here
removed most of legacy behaviour
<while> command :3
<choice><option scene="..."> supports commands block as well
Enabled textToHtml conversion for alert messages
function="execute" removed, tests are fixed
HTML formatting allowed at <displayname>
Let's proxy trigger "contextmenu" event to the bus and suppress it.
Merge pull request #20 from lolbot-iichan/develop

Various changes by lolbot-iichan. Thanks for contributing!