Refactor install.php

- Remove all references to update functions
- Improve step2 by checking if password exists (form) or mail (persona)
- Add a param($key, $default=falsse) function to get $_POST vars
- Fix coding style (mainly spaces)
Merge branch 'dev' into 411-update-system
Add basic system of update

- Check on update.freshrss.org for new updates
- Download script
- Apply script
- Need translations and verifications

NOTE: current script on server indicates version 0.7.3 is an update
of 0.8-dev ==> IT'S ONLY FOR MY TESTS!

Script just does a backup of ./data actually...

See https://github.com/marienfressinaud/FreshRSS/issues/411
Add translations for update system
Improve update API

Update script must implement 4 functions:
- apply_update() to perform the update (most important). Return true if
  all is ok, else false.
- need_info_update() returns true if we need more info for update, else
  false. If this function always returns false, you don't need to
  implement following functions (but it's better to not forget)
- ask_info_update() should be a HTML form to ask infos. Method must be
  post and action must point to _url('update', 'apply') (or leave it
  blank)
- save_info_update() is called for POST requests (to save form from
  ask_info_update())
Litlle improvements (update system)

- Check UPDATE_FILENAME exists before applying update
- Add empty line at the end of files
Merge branch 'dev' into 411-update-system
Update system now uses HTTPS connection

- Add some curl checks
- Refactor code
Add shortcuts

Add a shortcut to open the wiki. Shortcut is F1 and is not modifiable.

Add a shortcut to access user filters the same way to access share actions.
Fix category CSS

Before, when the category is closed by default, the active CSS class wasn't applied. Thus breaking the shortcuts for navigation.
Now it works the way it is supposed.
Merge pull request #593 from aledeg/fix-cat-css

Fix category CSS
Change wiki url
Add a link to filter categories

In the category configuration page, I added a filter link on each category. It works the same way than the "filter" link on the feed configuration page.

See #514
Merge pull request #595 from aledeg/filter-cat

Add a link to filter categories
Add configuration for help configuration
Fix Screwdriver theme

Before, it wasn't possible to hide categories when they had no articles to read.
I applied the same rule than the one described in here (https://github.com/marienfressinaud/FreshRSS/commit/d19824b919289ad63743f27da7861f2422da5baa).
Now, the categories are hidden when they have no articles to read.

See #594
Merge pull request #598 from aledeg/screwdriver

Fix Screwdriver theme
Bug referer for systems with non-standard HTTP port

Now tests also for the scheme and port, which must be identical to the
ones in the referer.

https://github.com/marienfressinaud/FreshRSS/issues/565#issuecomment-53916915
https://github.com/marienfressinaud/FreshRSS/issues/554
Add average on repartition charts.

It needs some verification on the value used to calculate the averages.
Add a first version of i18n for German

All the strings are not completed yet, but it's a good start!