Publish Titiler as metapackage

[vincentsarago]

We now have 3 namespaces packages: titiler.core, titiler.mosaic, titiler.application published on pypi with version 0.3.0

Having both old titiler==0.2.0 and the namespaces package with 0.3.0 is really confusing. As @kylebarron suggested we could publish a empty metapackage with the same version as the sub package.

[vincentsarago]

From slack:

• we're going to create a metapackage which strictly pin the sub package
• the metapackage will be published at least up to 1.0.0 (we can decide to deprecate it then)

[vincentsarago]

https://pypi.org/project/titiler/