Spaces -> tabs

Convert spaces to tabs.

If you want, I can also include in this pull request other files that need (re-)indenting:
```
$ git grep -l '^ ' | grep -v ^lib
LICENSE
api/index.php
atom-to-html.xsl
classes/dlg.php
classes/handler/public.php
classes/pref/feeds.php
css/tt-rss.css
images/indicator_white.gif
include/colors.php
include/functions.php
include/login_form.php
install/index.php
js/feedlist.js
js/functions.js
js/tt-rss.js
plugins/bookmarklets/init.php
schema/ttrss_schema_mysql.sql
schema/versions/mysql/101.sql
schema/versions/mysql/26.sql
schema/versions/mysql/69.sql
schema/versions/mysql/7.sql
schema/versions/mysql/84.sql
templates/digest_template.txt
templates/digest_template_html.txt
templates/email_article_template.txt
```

Not all of them need it (e.g., `LICENSE`, and probably the old schemas), but some of them (`js/*`, `include/*`, etc.) could use it.