PR: Create loading screen for the Dependencies widget, and added new icons for dependencies, debug, console-off and console-remote-off

[conradolandia]

Description of Changes

• Made a loading screen for the dependencies widget. Now it shows an animated spinner, an icon and a message while the dependencies are calculated.

New icons added to spyder/images

• console-off.svg
• console-remote-off.svg
• dependencies.svg
• debug.svg

Affirmation

By submitting this Pull Request or typing my (user)name below,
I affirm the Developer Certificate of Origin
with respect to all commits and content included in this PR,
and understand I am releasing the same under Spyder's MIT (Expat) license.

I certify the above statement is true and correct: @conradolandia

[ccordoba12]

Pretty nice improvements, thanks @conradolandia!

[ccordoba12]

@conradolandia, one thing that's missing is for you to actually use the new console-off icon in our code. For that, please go to this file:

spyder/spyder/api/shellconnect/main_widget.py

Lines 135 to 141 in 3f8eada

	widget = PaneEmptyWidget(
	self,
	"variable-explorer", # TODO: Use custom icon here
	_("No connected console"),
	_("The current console failed to start, so there is no "
	"content to show here.")
	)

replace variable-explorer by console-off in line 137 and remove the comment next to it.

[ccordoba12]

I really like the new icons. Great work @conradolandia!