Add .gitignore file under root directory
Change version number to 0.14.1 in README.md
Change versionName to 0.14.1 in manifest file
Change versionCode to 7
Change version number in AboutActivity
Change version number to 0.14.1 in LICENSES file
Fix preparePageJumping crash

The crash is caused by url being empty when first time opening a book.
When url is empty, preparePageJumping should do nothing.
This commit fixes the problem.
Release 0.14.1

* hotfix-0.14.1:
  Fix preparePageJumping crash
  Change version number to 0.14.1 in LICENSES file
  Change version number in AboutActivity
  Change versionCode to 7
  Change versionName to 0.14.1 in manifest file
  Change version number to 0.14.1 in README.md
  Add .gitignore file under root directory