Fix handling of save_show_or_return flags

[elfofmaxwell]

Fix #326

The following APIs are modified to accept 'save', 'show', 'return', 'both', and 'all':

• pl.cell_cycle_scores
• pl.connectivity_base
• pl.nneighbors
• pl.phase_portraits
• pl.dynamics
• pl.fate_bias
• pl.fate
• pl.least_action
• pl.bubble
• pl.nxvizPlot
• pl.arcPlot
• pl.hivePlot
• pl.basic_stats
• pl.show_fraction
• pl.variance_explained
• pl.biplot
• pl.loading
• pl.feature_genes
• pl.exp_by_groups
• pl.plot_direct_graph
• pl.scatters
• pl.show_landscape
• pl.cell_wise_vectors_3d
• pl.line_integral_conv
• pl.cell_wise_vectors
• pl.grid_vectors
• pl.streamline_plot
• pl.plot_energy
• pl.state_graph
• pl.plot_3d_streamtube
• pl.kinetic_curves
• pl.kinetic_heatmap
• pl.jacobian_kinetics acceptable value updated from save_fig to save
• pl.sensitivity_kinetics acceptable value updated from save_fig to save
• pl.plot_flow_field
• pl.plot_nullclines
• pl.plot_fixed_points_2d
• pl.plot_fixed_points
• pl.plot_traj
• pl.plot_separatrix
• pl.topography
• pl.jacobian
• pl.jacobian_heatmap
• pl.sensitivity
• pl.sensitivity_heatmap

The following APIs now only accept 'save', 'show', 'both' and would support 'return', 'all' in future:

• pl.response
• pl.plot_hill_function
• pl.causality
• pl.comb_logic
• pl.hessian
• pl.lap_min_time

The following APIs rely on previously mentioned APIs and accept 'save', 'show', 'return', 'both', and 'all' as kwargs:

• pl.infomap
• pl.leiden
• pl.louvain
• pl.pca
• pl.trimap
• pl.tsne
• pl.umap
• pl.space
• pl.acceleration
• pl.curl
• pl.curvature
• pl.divergence
• pl.speed