Add helper methods to Type

[letmutx]

We can start with the following:

• Type checks
  • is_primitive
  • is_array
  • is_reference_type (arrays and classes)
  • is_class
  • is_int
  • is_float
  • is_double
  • is_char
  • is_byte
  • is_short
  • is_long
  • is_boolean
• to_java_type - return the java representation of a type.
  ex: Ljava/lang/String; -> java.lang.String, [B -> byte[] etc.
• Add constants representing smali types and replace all usages.
  ex: const BYTE: &str = "B" etc.