I can finally stop complaining about the absence of a emoji picker for Linux. Now there is the EmojiOne Picker! It is a simple picker application based on the awesome emoji set of EmojiOne.
$ sudo add-apt-repository ppa:ys/emojione-picker
$ sudo apt update
$ sudo apt install emojione-picker
To use just type EmojiOne Picker at the Dash. Note that it takes a few seconds to load and finally settles down in the system tray area with a smiley face. Right-click on it to get the fully detailed list of emoji. Click on any one and it will be copied to your clipboard for easy pasting into any app or website.
In Settings, I like to choose the Low end computer mode which reduces the number of emoji and thus makes loading and usage of this app faster.
You can also right-click and choose Search to filter emoji by typing a word describing it. This is useful to find obscure emoji.
Tried with: EmojiOne Picker 0.1 and Ubuntu 16.04