Allow to sync unittests while they are not declared in plugin.xml

[el-teedee]

Since sync is based on plugin.xml parsing, unittests are no longer synced.
Allow to sync unittests (or any other directory, or files) between plugin and webapp, event if it is not declared in plugin.xml.
Such a directory could be voluntary not declared for it NOT to be packaged in a plugin.zip.

Workaround :

• declare package unittests in plugin.xml lusing:
• preview and perform Sync (unittests are synced)
• remove package declaration