fix(parser): changes parser to throw an error when it encounters an unexpected token

Change the handling of unexpected tokens. Make the parser throw the "is an unexpected token" exception, so ExpressionVisitor won't throw confusing "Can not watch expression containing ';'".

Closes #830

Closes #905

Author: vsavkin

lib/core/parser/dynamic_parser_impl.dart

@@ -40,6 +40,9 @@ class DynamicParserImpl {
       if (isChain && expr is Filter) {
         error('Cannot have a filter in a chain');
       }
+      if (!isChain && index < tokens.length) {
+        error("'${next}' is an unexpected token", index);
+      }
     }
     return (expressions.length == 1)
         ? expressions.first

test/core/parser/parser_spec.dart

@@ -194,6 +194,10 @@ main() {
         expectEval("4()").toThrow('4 is not a function');
       });
 
+      it("should throw on an unexpected token", (){
+        expectEval("[1,2] trac")
+            .toThrow('Parser Error: \'trac\' is an unexpected token at column 7 in [[1,2] trac]');
+      });
 
       it('should fail gracefully when invoking non-function', () {
         expect(() {