fix .travis.yml failing with bldr

and fix secure bldr-task to run on Windows
first steps into using the GitHelper
move git executions from PullRequestMergeCommand
move git executions from BranchDeleteCommand
move git executions from BranchPushCommand
move git executions from BranchRemoteAddCommand
move git executions from BranchSyncCommand
move git executions from IssueTakeCommand
move git executions from PullRequestFixerCommand
move git executions from PullRequestSwitchBaseCommand
improve switching pull-request base command

- Switch base in active pull request (when supported by adapter)
  else create a new PR with the same information (but new base)
- Inform if a new PR was made during the base-switch
- Abort git rebase process on failure
move git executions from PullRequestSquashCommand

As a little bonus this will preserve the original first-subject
move git-sync logic to GitHelper from BranchSyncCommand
reduce duplication in GitHelper
move git executions from PullRequestSemVerCommand

And don't checkout as we can use the branch-reference!
move git executions from FabbotIoCommand
make BranchChangelogCommand more robust
fix test for BranchDeleteCommand
fix tests for BranchForkCommand
fix test for BranchPushCommand