fix: Issue #70 - No static in global + hassle free Multi SideMenu support + Segregated controller from global +Animated Container issue

[aditya113141]

New version release possible

I believe that if the changes pass tests successfully on your side then you can release a new version
with Multiple sideMenus support. Let me know if any edits are needed

• This PR solves all the issues related with use of multiple sideMenus at the same time. Issue #70
  Solved the issue of static variables in global which were causing hindrance for
  multiple sidemenus to function without sharing their variables
• Detailed work on removing static nature can be found in this comment
• Due to rapid toggling, the AnimatedContainer in sidemenu.dart was getting into weird state. Fixed it here
• Segregated controller from global.dart and fixed the export files. No need of exporting global.dart

[Jamalianpour]

Thank you @aditya113141
Can you update example and readme with this changes?

[aditya113141]

@Jamalianpour There is no change required in example. I ran it on my side. There is no issue. I have made changes to the code in a way that the syntax for the developer doesn't changes. Developer can write the code according to documentation of previous version. In readme file, the only change needed is the version of library, if you decide to release a new version with this PR. Otherwise, no change in usage and syntax.

[Jamalianpour]

@aditya113141 Sorry, but I have to revert your code because you don't follow flutter/dart lint