Template secrets and joins

[tiparega]

Issue #43

Description of changes:
I added few changes over @martinhaus commits.

• I merged current master branch
• One is to not override main secret, as that one in json format is used if no change is detected (specially interesting for sync).
• The other is I added the option to join all templated secrets into one file. I needed because I was mixing some secrets into a single YAML file.

It's properly working, but I don't know Golang and I didn't changed tests, so code can surely be improved.

[yrsurya]

is there any ETA when can we get this feature available?