Seed the random generator from offline command line

[KristianKarl]

When running the CLI using the offline command, a new option:
--seed or -d can be used to seed the random generator.

Example:

java -jar graphwalker-cli-4.2.0-SNAPSHOT.jar offline --seed 147945811993279 --model model.json "random(edge_coverage(100))" 

[codecov-io]

Codecov Report

Merging #223 into master will decrease coverage by 0.04%.
The diff coverage is 20%.

@@             Coverage Diff              @@
##             master     #223      +/-   ##
============================================
- Coverage     76.01%   75.97%   -0.05%     
- Complexity     1196     1197       +1     
============================================
  Files           129      129              
  Lines          4402     4407       +5     
  Branches        661      663       +2     
============================================
+ Hits           3346     3348       +2     
- Misses          821      823       +2     
- Partials        235      236       +1