Fix debian/copyright format for empty-short-license-in-dep5-copyright

Lintian reports empty-short-license-in-dep5-copyright warnings.
The License field in debian/copyright should not be empty by dep5 standard.
This commit adds the missing empty field.

Signed-off-by: Ying-Chun Liu (PaulLiu) <paulliu@debian.org>
Use system libjs-excanvas

In Debian, there's system-wide libjs-excanvas. This commit makes
tribler to use excanvas.js from system instead of local one.

Signed-off-by: Ying-Chun Liu (PaulLiu) <paulliu@debian.org>
Merge pull request #860 from grandpaul/fix-copyright-format

Fix debian/copyright format for empty-short-license-in-dep5-copyright
Revert libx11-6 back in debian/control Depends.
Merge pull request #861 from grandpaul/use-system-libjs-excanvas

Use system libjs-excanvas
remove safe_dict
create new SQLiteDB base module
create new SQLiteDB upgrade module
remove old SQLiteCacheDBBase
remove old stuff
fix database
fix db upgrade
fix db tests