Fixed bookshelves related bugs

[satyamtg]

This PR does the following -

• Fixes #106 - Correct the showing and hiding of the "Go to bookshelves" link
• Fixes #107
• Fixes #105
• Fixes #108

To make it easier to review -

• Changes related to fixing #106 are in gutenbergtozim/templates/base.html and in lines 982, 999 in gutenbergtozim/export.py

[rgaudin]

Don't mix formatting and bug-fix otherwise this PR will have to be reviewed commit-by-commit !!!

Send a formatting-only PR first that we'll merge so that this becomes bug-fix only.

[satyamtg]

Don't mix formatting and bug-fix otherwise this PR will have to be reviewed commit-by-commit !!!

Send a formatting-only PR first that we'll merge so that this becomes bug-fix only.

Created #111 which only adds black formatting to python files

[rgaudin]

Another thing I just discovered ; could you please integrate this as well (so that we don't have static English strings there):

diff --git i/gutenbergtozim/templates/bookshelf.html w/gutenbergtozim/templates/bookshelf.html
index 593fd73..ac3298c 100644
--- i/gutenbergtozim/templates/bookshelf.html
+++ w/gutenbergtozim/templates/bookshelf.html
@@ -1,7 +1,7 @@
 {% extends "base.html" %}
-{% block title %}Individual Bookshelf{% endblock %}
+{% block title %}{{ bookshelf }}{% endblock %}
 {% block content %}
-<h1 class="table-title">{{ bookshelf }} Bookshelf</h1>
+<h1 class="table-title">{{ bookshelf }}</h1>
 <table class="data-table display" cellpadding="0" cellspacing="0" border="0" id="books_table"></table>
 <script type="text/javascript">

[rgaudin]

There's no review requested but I checked the rest and it's OK. We'll merge once you fix those strings in the template.