Issue-93: Support for persistent values.

[shomaglasang]

• Support for persistent MQTT message when publishing updates/writes to AI, AO, AV, BI, BO and BV property name, present value and priority array.
• Set the object property name, present value and priority array to the last published values when bacnet server starts up.
• Fix the format of the priority array value in the payload into a valid json format. From

  { "value" : "{123.500000,Null,Null,Null,Null,Null,Null,Null,Null,300.000000,Null,Null,Null,Null,Null,222.300003}" , "uuid" : "" }

  into

  { "value" : ["123.500000","Null","Null","Null","Null","Null","Null","Null","Null","300.000000","Null","Null","Null","Null","Null","222.300003"] , "uuid" : "" }

[RaiBnod]

FYI in the future, we'll be releasing v<major>.<minor>.<patch>-rc.<number> instead of v<major>.<minor>.<patch>-rc<number>. This is because our program treats v1.1.1-rc9 > v1.1.1-rc10 but v1.1.1-rc.9 < v1.1.1-rc.10.