Update signature presentation in pinfo classes

classes:

- init definition comes before class docstring
- remove Constructor info block, because it no longer has multiple entries
- don't include instance call definition as definition

objects:

- don't duplicate call def and definition in callables


Before:

```
In [2]: pinfo C
Type:       type
String Form:<class '__main__.C'>
Definition: C(self, call)
Docstring:  class docstring
Constructor information:
 Definition:C(self, a=5)
 Docstring:     init docstring

In [3]: pinfo c
Type:       C
String Form:<__main__.C object at 0x10ee5e410>
Definition: c(self, call)
Docstring:  class docstring
Constructor docstring:init docstring
Call def:   c(self, call)
Call docstring:call docstring
```

After:

```
In [2]: pinfo C
Type:            type
String form:     <class '__main__.C'>
Init definition: C(self, a=5)
Docstring:       class docstring
Init docstring:  init docstring

In [3]: pinfo c
Type:           C
String form:    <__main__.C object at 0x102e23510>
Definition:     c(self, call)
Docstring:      class docstring
Init docstring: init docstring
Call docstring: call docstring
```