MRG, MAINT: More deprecations and bumps

[larsoner]

Not all of the deprecations, but takes care of:

• Version bumps for 2-year-at-time-of-release deps
• mne.fixes removals for bumped versions (mostly _import_fft -> from scipy.ft import)
• mne.connectivity
• mne.datasets.*.has_dataset
• mne.inverse_sparse prox solver

I'll open another PR with more soon enough.