[Web UI] Reorder top plugins like in the curse interface

[Web UI] Update keyboard shortcuts

* remove all shortcuts not implemented yet in web UI
* implement show/hide Docker stats shortcut
* implement show/hide processes stats

[Web UI] Network cumulative/combination

Handle cumulative and combination mode for network I/O
Fix shortcuts for cumulative and combination
Use bit/s for network I/O

Hide empty sensors in web ui

[Web UI] Big refactoring

Move logic from controller and views to the new services GlancesStats and GlancesPlugins : GlanceStats load data from api and set data in plugins. Plugins are responsible for transforming data for the view.
GetAlert is now in GlancesPlugin
Use view data instead of getAlert when is possible
Remove directives for monitor plugin

[Web UI] Fix debug mode

[Web UI] Warn user if the server is down/disconnected

[Web UI] Help page responsive on small screen

Fix UTF-8 characters being output on latin1 terminals

This fix translates the characters to an appropriate encoding for the
terminal. "°C" (A acute, degrees, C) was being output on latin1
terminals, which is a bug since the LC_CTYPE locale setting should tell
the program whether it's okay to output Unicode.

This follows the recommendation from the official curses library
documentation: https://docs.python.org/2/library/curses.html

Steps to reproduce the issue:

1. Install pysensors, enable any kernel modules necessary to support it
2. Run `LANG=en_US rxvt -e glances`
3. Look in SENSORS section

The corrupt Unicode character sequence will appear.

News --disable-quicklook, --disable-cpu, --disable-mem, --disable-swap, --disable-load tags (issue #631)

unittest: virtualenv support