fix a minor cursor restore bug

Add a feature to draw a box easier

Fixed scroll zoom on nonprimary monitor or in small window

Fix a bug: creating a box with one point

fix a bug to select a small bounding box

fix a bug of disabled edit and delete menu in the label list menu

Prevent the crash

Adding the path to '.settings.pkl' file, this is especailly useful for MacOS. Then we can put '.settings.pkl' into 'MacOS' folder within 'labelImg.app'. The App will crash without path setting, as soon as we close the App in MacOS.

Enhance compatibility

Adding the path to 'data' folder, this is especailly useful for Mac OSX.
Then we can put the 'data' folder into 'MacOS' folder within 'labelImg.app'.

Enhance compatibility

With Anaconda3-4.4.0-Windows-x86_64 in Win 8 & 10, encoding name "utf8" will lead to error.  We change the encoding name to "utf-8", it's OK. Very strange, we do not know why.

Made spelling corrections to variables

Fix filename bug

If the file name contains ".", it will go wrong.  e.g. hello.world.jpg --> hello.xml

Fixed usage of deprecated function