Reduce docker images size of doichain/dapp

[NiKrause]

Based of the analyzis of #139
please create new improved Dockerfile in order to reduce the docker image size.
Please use branch 0.0.9!

[jay-dee7]

hey @inspiraluna i think it would be safe to remove the doichain-core source code related directory after the build process is done?
i'm refering to this content after make install since after make, the compiled code goes in /usr/local/bin/ and we don't really need the source at all:

[NiKrause]

yes, I guess thats a good idea. In the beginning we were often doing hot code fixes inside the image and compiled it afterwards again. But now it could truly be removed.!

[jay-dee7]

@inspiraluna i tried removing it, however it didn't help much with reducing the size at all. It's taking longer than what i anticipated :(

[jay-dee7]

@inspiraluna i've created a new PR here --> added alpine docker image, which reduces the size of the docker image from 1.7GB to 968MB. I have also added a doc, which explains about how to build the alpine image and also how to run the resulting image --> how to guide for alpine image