wendelin.core: Add part/recipe how to build it from git repository

There is now

    wendelin.core       and
    wendelin.core-dev

parts.

wendelin.core just installs released egg from pypi, and
wendelin.core-dev installs it from latest git version.

A reminder how to use wendelin.core-dev instead of wendelin.core:

if your buildout.cfg

    [buildout]
        # directly or indirectly
        extends = ..../wendelin.core/buildout.cfg

then at tails, do

    [buildout]
        parts -= wendelin.core
        parts += wendelin.core-dev

This way wendelin.core will be fetched from git repository.

component/wendelin.core/buildout.cfg

@@ -2,6 +2,31 @@
 parts =
   wendelin.core
 
+
+# wendelin.core installed from released egg from pypi
 [wendelin.core]
 recipe = zc.recipe.egg:custom
 egg = wendelin.core
+
+
+# wendelin.core installed from latest git version
+[wendelin.core-dev]
+recipe = zc.recipe.egg:develop
+setup = ${wendelin.core-repository-submoduleinit:location}
+
+
+[wendelin.core-repository]
+recipe  = slapos.recipe.build:gitclone
+repository = https://lab.nexedi.cn/nexedi/wendelin.core.git
+# dir is pretty name as top-level -dev recipe
+location = ${buildout:parts-directory}/wendelin.core-dev
+
+
+# TODO add `git clone --recursive` to slapos.recipe.build:gitclone
+#      and this way merge this -submoduleinit into -repository part
+[wendelin.core-repository-submoduleinit]
+recipe = plone.recipe.command
+command = cd "${wendelin.core-repository:location}" && git submodule update --init
+stop-on-error = true
+# propagate location of main repo
+location= ${wendelin.core-repository:location}