Remove edition and publication year fields from Model
Fix typos and necessary files not sent in last commit
Fix not sent views.py from the last commit and add edit.html stub
Fix __str__ method for BookType Model
Make "Edit book" views' fields filled on rendering the page

- Also fix an error that caused Add book view to raise error when there were errors in validating the form
More improvements on Book form

- Remove some redundant code
- Change type of Price field in Model to DecimalField
Implement book editing
Make remove view raising 404 when no items are found

- It was showing "Nothing to display" message before
Add Bulk actions to book index

- Improve UI a little bit (table-responsive)
- Small changes in base template
Fix an error during removing multiple books
Add Categories app stub
Create a Sell app stub
Implement initial version of personal data form in Sell app

Issue: gh-7
Polishing Personal data form in Sell app

Resolves gh-7
Fix KeyError in Provide personal data form
Fix a bug that caused Add book form to redirect to /sell

- Also unified urls.py and reverse() style
Create Book list base template to reduce redundant code
Make Book list template more flexible
Change "book.id" to "book.pk"
Add an initial UI of selling books form

gh-6