Update version and add sign

This is a continuation of PR #8.

I  reverted an excessive correction.
This was carried out only to a signature and hanlder change and version-up. 

The main change is the followings.:
* Update tycho version 0.20.0.
* Update minimum Java version to 1.7
* Use commands instead of action
* Add profile for sign and explain in README.md

Was in 'maven-dependency-plugin section' of PR # 8, section, I have deleted.
The reason for having added this processing is the following. 
Since jar which has dependence in generated jar was not contained even if it call 'package' after 'eclipse:eclipse'. 
I do not know the dependence of solutions that in m2e on the tycho. Also, I do not have the confidence that you use the "maven-dependency-plugin" is correct. 
So, it is not included this time.