Finding the gedit plugin folder

First, I'll answer the question about the specific plugins. gedit-developer-plugins is available in the official Ubuntu archive, and I'd suggest installing it from there. clickconfig, on the other hand, unfortunately does not seem to have been ported to to Gedit 3 and is not compatible.

More generally, for Gedit 3 (which is in Ubuntu 11.10 and above) local plugins should be installed to ~/.local/share/gedit/plugins The .plugin file must be in that exact directory, sub-directories are not scanned. For instance, here's the file layout of mine:

$ tree ~/.local/share/gedit/plugins/
/home/andrew/.local/share/gedit/plugins/
├── markdown-preview
│   ├── __init__.py
│   ├── __init__.pyc
│   └── locale
│       └── fr
│           └── LC_MESSAGES
│               └── markdown-preview.mo
├── markdown-preview.plugin
├── reSt-preview
│   ├── __init__.py
│   └── __init__.pyc
└── reSt-preview.plugin

From the official docs on the gedit website, the folder is: /home/username/.local/share/gedit/plugins. If this folder does not exist, you will have to create it