Changed the way of calculating the mouse position when the drag event ends

- Added dragging images
- Default values for settings page

Added the ability of opening new tabs next to the current one or not

Added the ability to name the query urls in the settings page

Added a hint in top left corner of the content to know what url is used while dragging a text

There isn't a trusty way to determine the location in screen pixels of the viewport (content of the website), so for now it only checks if the the drag operation has been inside window browser window in order to cancel opening a new tab or not.

Dragging into bookmark toolbars, address toolbar, ... will always open the dragged link or text in a new tab, until Mozilla fixes or adds the functions needed to fix this problem.

dragend.clientX/Y is always 0
mozInnerScreenX/Y depends of user zoom
element.getBoundingClientRect() doesn't give the location in screen
window.innerheight/outerheight are useless to determine a trusty viewport location in screen

Check if the drag operation has been inside the page content before opening a new tab

Added option to swap foreground/background behavior

Changed the time when the add-on is loaded, now is at document_start, not at document_idle
I did a mess with versions, so now i start with 1.3

i swapped the up and down, with down and up by error - fixed

Dragging selected text support enabled

now works with file system opened files