Remove use of section property from Package

[tonyskapunk]

• Remove the use of Package.section for the use of Version.section

Fix: #80

---

apt 1.9 is in experimental, likely will be included in buster coming release:

$ for c in experimental buster u19.04 u18.04 u16.04; do
    echo ${c} ===
    docker exec ${c} \
        python3 -c \
            'import apt; ac=apt.Cache(); print(ac["python3-apt"].candidate.version)';
done
=== experimental ===
1.9.0
=== buster ===
1.8.4
=== u19.04 ===
1.8.4
=== u18.04 ===
1.6.4
=== u16.04 ===
1.1.0~beta1ubuntu0.16.04.5

Here testing with the current code that uses Package.section showing that will fail in 1.9

$ for c in experimental buster u19.04 u18.04 u16.04; do
    echo === ${c} ===
    docker exec ${c} \
    python3 -c \
        'import apt; ac=apt.Cache(); print(ac["python3-apt"].section)'
done
=== experimental ===
Traceback (most recent call last):
  File "<string>", line 1, in <module>
AttributeError: 'Package' object has no attribute 'section'
=== buster ===
python
=== u19.04 ===
python
=== u18.04 ===
python
=== u16.04 ===
python

Here using Version.section instead (note that candidates produces a Version object):

$ for c in experimental buster u19.04 u18.04 u16.04; do
    echo === ${c} ===
    docker exec ${c} \
        python3 -c \
            'import apt; ac=apt.Cache(); print(ac["python3-apt"].candidate.section)'; done
=== experimental ===
python
=== buster ===
python
=== u19.04 ===
python
=== u18.04 ===
python
=== u16.04 ===
python

[tonyskapunk]

Merging this one