Added support for bokeh #298

[giswqs]

This PR adds bokeh as a new plotting backend. Currently, it supports adding basemaps, loading COG and local raster datasets. Supporting for loading vector data is in progress.

import leafmap.bokehmap as leafmap
m = leafmap.Map()
m.add_basemap('ROADMAP')
url = 'https://opendata.digitalglobe.com/events/california-fire-2020/pre-event/2018-02-16/pine-gulch-fire20/1030010076004E00.tif'
m.add_cog_layer(url)
m

[lgtm-com]

This pull request introduces 11 alerts when merging c355a18 into 71d1b4d - view on LGTM.com

new alerts:

• 10 for Modification of parameter with default
• 1 for 'import *' may pollute namespace

[giswqs]

Added support for STAC.

import leafmap.bokehmap as leafmap
m = leafmap.Map()
url = 'https://canada-spot-ortho.s3.amazonaws.com/canada_spot_orthoimages/canada_spot5_orthoimages/S5_2007/S5_11055_6057_20070622/S5_11055_6057_20070622.json'
m.add_stac_layer(url, bands=['B3', 'B2', 'B1'])
m

[lgtm-com]

This pull request introduces 11 alerts when merging cc5d387 into 71d1b4d - view on LGTM.com

new alerts:

• 10 for Modification of parameter with default
• 1 for 'import *' may pollute namespace

[giswqs]

Added support for loading vector data (e.g., GeoDataFrame, Shapefile, GeoJSON, etc.).

import leafmap.bokehmap as leafmap
m = leafmap.Map()
m.add_basemap('OpenTopoMap')
url = 'https://github.com/giswqs/leafmap/blob/master/examples/data/cable_geo.geojson'
m.add_vector(url, line_color='blue', line_width=2)
m

[giswqs]

Visualizing vector data with custom colors.

import leafmap.bokehmap as leafmap
m = leafmap.Map()
m.add_basemap('CartoDB.DarkMatter')
url = 'https://raw.githubusercontent.com/telegeography/www.submarinecablemap.com/master/web/public/api/v3/cable/cable-geo.json'
m.add_vector(url, line_color='color', line_width=2)
m

[lgtm-com]

This pull request introduces 11 alerts when merging 3028c50 into 71d1b4d - view on LGTM.com

new alerts:

• 10 for Modification of parameter with default
• 1 for 'import *' may pollute namespace

[lgtm-com]

This pull request introduces 11 alerts when merging 0300488 into 71d1b4d - view on LGTM.com

new alerts:

• 10 for Modification of parameter with default
• 1 for 'import *' may pollute namespace

[lgtm-com]

This pull request introduces 11 alerts when merging ab4e4a5 into 71d1b4d - view on LGTM.com

new alerts:

• 10 for Modification of parameter with default
• 1 for 'import *' may pollute namespace

[lgtm-com]

This pull request introduces 14 alerts when merging d8f049a into 71d1b4d - view on LGTM.com

new alerts:

• 10 for Modification of parameter with default
• 1 for Module is imported more than once
• 1 for Unused local variable
• 1 for 'import *' may pollute namespace
• 1 for Variable defined multiple times