CLI: improve diagnostic message format

- render the whole line where the error/warning points to, if any, and another
  line with '^', like other compilers do
- lowercase diagnostic severity
- decapitalize the message if it doesn't start with a proper name

compiler/testData/integration/ant/js/verbose/build.log.expected

@@ -3,8 +3,8 @@ Buildfile: [TestData]/build.xml
 
 build:
 [kotlin2js] Compiling [[TestData]/root1] => [[Temp]/out.js]
-[kotlin2js] LOGGING: Compiling source files: [TestData]/root1/foo.kt
-[kotlin2js] OUTPUT: Output:
+[kotlin2js] logging: compiling source files: [TestData]/root1/foo.kt
+[kotlin2js] output: output:
 [kotlin2js] [Temp]/out.js
 [kotlin2js] Sources:
 [kotlin2js] [TestData]/root1/foo.kt