ENH: Added new type FeatureTable[Normalized]

[VinzentRisch]

solves #339

Adds new typed called FeatureTable[Normalized].

Run it locally

1. First, clone the repo and checkout the PR branch:

git clone https://github.com/qiime/q2-types.git
cd q2-types
git fetch origin pull/340/head:pr-340
git checkout pr-340
pip install -e .

2. Download test files
   feature-table.biom.zip

3. Test it out!

qiime tools import --input-path feature-table.biom --output-path feature_table.qza --type "FeatureTable[Normalized]"

[ebolyen]

Thanks @VinzentRisch!