Update Main.java

add max and min angle control
Update RandomPolygonGen.java

add max and min angle property
add file angle_helper.java

add file angle_helper.java
this file contains a seriers of functoins about angle.
add function getAngle to calc the degree of angle by using vector
method.
add max and min angle control

add max and min angle control  while  the polygons are  generatered
Merge pull request #2 from Sunlike/master

add max and min angle condition to ui