app: loading saved proxies data
po: updating translatable files
utils: improved file creation

removed vala warning
app: update proxies on delete one
misc: fixing emacs mode to use always space
row: added ProxyData property

utils: added public ProxyData struct definition
window: use Row::proxy_data property
window: fix some whitespace issue. Note: This should not be part of this commit but
git is tricking not accepting the patch properly without it
misc: whitespace and indentation fix
row: prevent double emit of activate signal
app: added initial default-plugin impl
misc: removed print debugging calls
app: added external plugins initial impl

Plugins are read from folders inside $XDG_DATA_DIR/gproxies.
Inside are at least a plugin.ini file with the following contents:

--------------
[Plugin]
name = blah
exec = blah.sh
--------------

The Plugin.name key should match the name of the plugin folder
The Plugin.exec key should have the relative path of the script to execute
More details in PLUGINS.md file
docs: added initial plugins documentation
plugins: moved plugins call to another thread

Plugins execution call can block on the interface. Therefore
I'm moving those to a new different thread.
app: blocking UI when executing plugins code
plugins: add user/password to plugin call when set