Improve state presentation symbol extract logic

[jsetton]

This also fixes the below exception error, introduced with #265, caused by users who have invalid state presentation format defined on some of their Alexa-linked items.

SyntaxError: [sprintf] unexpected placeholder
    at sprintf_parse (/var/task/node_modules/sprintf-js/src/sprintf.js:202:23)
    at sprintf (/var/task/node_modules/sprintf-js/src/sprintf.js:26:31)
    at Object.temperature (/var/task/alexa/propertyMap.js:214:17)
    at item.metadata.alexa.value.split.forEach (/var/task/alexa/propertyMap.js:431:52)
    at Array.forEach (<anonymous>)
    at AlexaPropertyMap.addItem (/var/task/alexa/propertyMap.js:362:42)
    at items.filter.forEach (/var/task/alexa/v3/discovery.js:81:29)
    at Array.forEach (<anonymous>)
    at item.metadata.alexa.value.split.some (/var/task/alexa/v3/discovery.js:77:77)
    at Array.some (<anonymous>)