Implements sidebar's Archive

modified:   blog/assets/css/main.css
modified:   blog/assets/css/main.sass
modified:   blog/templates/base.html
modified:   blog/templates/details.html
modified:   blog/templates/index.html
new file:   blog/templatetags/__init__.py
new file:   blog/templatetags/custom_filters.py
modified:   blog/views.py