Add native uuid module.

uuid module provides v4() function which returns a type 4 (pseudo randomly
generated) UUID in string.
Make ScriptableDocument support JSON.stringify.
Fix style errors.

This patch fixes below style errrors.

error file=/home/sloan/workspace/beyond/core/app/beyond/engine/javascript/lib/database/ScriptableQuery.scala message=Method name does not match the regular expression '^[a-z][A-Za-z0-9]*$' line=16 column=6
error file=/home/sloan/workspace/beyond/core/app/beyond/engine/javascript/lib/ScriptableUUID.scala message=Method name does not match the regular expression '^[a-z][A-Za-z0-9]*$' line=11 column=6
error file=/home/sloan/workspace/beyond/core/app/beyond/engine/javascript/lib/ScriptableFuture.scala message=Method name does not match the regular expression '^[a-z][A-Za-z0-9]*$' line=30 column=6
error file=/home/sloan/workspace/beyond/core/app/beyond/engine/javascript/lib/ScriptableFuture.scala message=Method name does not match the regular expression '^[a-z][A-Za-z0-9]*$' line=35 column=6
error file=/home/sloan/workspace/beyond/core/app/beyond/engine/javascript/lib/ScriptableFuture.scala message=Method name does not match the regular expression '^[a-z][A-Za-z0-9]*$' line=42 column=6
error file=/home/sloan/workspace/beyond/core/app/beyond/engine/javascript/lib/ScriptableFuture.scala message=Method name does not match the regular expression '^[a-z][A-Za-z0-9]*$' line=49 column=6
error file=/home/sloan/workspace/beyond/core/app/beyond/engine/javascript/lib/ScriptableFuture.scala message=Method name does not match the regular expression '^[a-z][A-Za-z0-9]*$' line=79 column=6
error file=/home/sloan/workspace/beyond/core/app/beyond/engine/javascript/lib/ScriptableFuture.scala message=Method name does not match the regular expression '^[a-z][A-Za-z0-9]*$' line=94 column=6
error file=/home/sloan/workspace/beyond/core/app/beyond/engine/javascript/lib/ScriptableFuture.scala message=Method name does not match the regular expression '^[a-z][A-Za-z0-9]*$' line=105 column=6
error file=/home/sloan/workspace/beyond/core/app/beyond/engine/javascript/lib/ScriptableFuture.scala message=Method name does not match the regular expression '^[a-z][A-Za-z0-9]*$' line=128 column=6
error file=/home/sloan/workspace/beyond/core/app/beyond/engine/javascript/lib/ScriptableFuture.scala message=Method name does not match the regular expression '^[a-z][A-Za-z0-9]*$' line=140 column=6
error file=/home/sloan/workspace/beyond/core/app/beyond/engine/javascript/lib/ScriptableFuture.scala message=Method name does not match the regular expression '^[a-z][A-Za-z0-9]*$' line=155 column=6
error file=/home/sloan/workspace/beyond/core/app/beyond/engine/javascript/lib/ScriptableConsole.scala message=Method name does not match the regular expression '^[a-z][A-Za-z0-9]*$' line=11 column=6
error file=/home/sloan/workspace/beyond/core/app/beyond/engine/javascript/lib/ScriptableConsole.scala message=Method name does not match the regular expression '^[a-z][A-Za-z0-9]*$' line=15 column=6
error file=/home/sloan/workspace/beyond/core/app/beyond/engine/javascript/lib/ScriptableConsole.scala message=Method name does not match the regular expression '^[a-z][A-Za-z0-9]*$' line=19 column=6
error file=/home/sloan/workspace/beyond/core/app/beyond/engine/javascript/lib/ScriptableConsole.scala message=Method name does not match the regular expression '^[a-z][A-Za-z0-9]*$' line=23 column=6
error file=/home/sloan/workspace/beyond/core/app/beyond/engine/javascript/lib/ScriptableConsole.scala message=Method name does not match the regular expression '^[a-z][A-Za-z0-9]*$' line=27 column=6
Implement ScriptableFileSystem.

It's an interface to provide JavaScript API for handling file system.
Now only basic functions are implemented to read and write files.
The API design is found in the Wiki page below.

https://github.com/SollmoStudio/beyond/wiki/Beyond-File-System-API