Insert an image directly from filesystem

[DanielVenturini]

Hello, nice software.

I guess the retex would be great if it allows insert image directly by filesystem. The first commit allows to open a select box and get the image path, that is, selecting an image results in:
![Alt text](/home/user/path/to/image.png).

The second commit create a menu bar called Insert with the Tables and Image as sub-menus, where Image uses the function written at first commit. The Tables sub-menus (Insert table and Table editing mode) were in Edit menu, and it doesn't make much sense, I guess. Then, I removed those and inserted in Insert menu.

[mitya57]

Thanks for your contribution! I have left some comments.

[DanielVenturini]

So, I revert my first commit, that is, I undo the Insert menu. Then, the Insert images by file path is in Edit menu and uses getOpenFileNames to allows the user add more than one image at same import. For the last, I splet into a function to get the correct syntax and turned it in a static method to access in both files.

[DanielVenturini]

Great. Thank you.