[Enhancement] Add "Delete Notes" option to the list view and multi-note selection on desktop

[Softvision-MariusComan]

[Notes]:

• Right now the only method to delete a note is to open it, click on the menu button from the right side of the title and select the "Delete Note" option. This takes a lot of time if you want to delete multiple notes. Considering this I think that we should add multiple note selection on the list view and also we should be able to delete a note without opening it.
• We could implement the same note selection method as in the mobile app, where there is a dash (-), in front of the note's title, that can be clicked in order to select the note.
• Also, another method to delete a note from the list view could be right clicking on it and selecting the "Delete" option from a context menu (eg. the custom context menu created for the "Tab Center Redux" add-on).

[Affected versions]:

• Firefox 61.0.1 and above

[Affected Platforms]:

• All Windows
• All Linux
• All Mac

[Prerequisites]:

• Have a new Firefox profile with the latest version of the "Firefox Notes" add-on (4.2.0dev), custom built on 18.07.2018, installed.
• Have at least a note in the sidebar.
• The "Notes" sidebar is in the list view.

[Steps to reproduce]:

1. Open the browser with the profile from prerequisites.
2. Long click on any note and observe the behavior.

[Expected result]:

• The note is selected.

[Actual result]:

• The note is opened.

[Additional Notes]:

• Attached a screen recording of the issue: