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.
Change wiki url
Add configuration for help configuration
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!
Fix collapse shortcut behavior

Before, the collapse shortcut was marking all articles as read when used. No matter what configuration you use.
Now, the collapse shortcut marks articles only if the appropriate configuration is used (when article is viewed).
Merge pull request #605 from aledeg/autoread

Fix collapse shortcut behavior
Merge pull request #600 from aledeg/average

Add average on repartition charts.
Merge pull request #592 from aledeg/more-shortcuts

Add shortcuts
Bug HTML stats

Categories containing a space were not displayed properly
https://github.com/marienfressinaud/FreshRSS/issues/547
Fix navigation on hidden categories and feeds

Before, when navigating with the keyboard, hidden categories and feeds where shown.
Now, they stay hidden.

See #604
Merge pull request #606 from aledeg/navigation

Fix navigation on hidden categories and feeds