Improved logo with transparent background

[shirubana]

Improved logo with transparent background
(115775-Solar Rd Tools Logo Design_horizontal.png is the one with trasparent background but it has crappy resolution)
same logo and resolution as docs>sphinx>source>images>logo_horizontal_highres.png but with transparent background (I would perhaps place it in that folder instead)

• [ x ] Code changes are covered by tests
• [ x ] Code changes have been evaluated for compatibility/integration with TrendAnalysis
• [ x] New functions added to __init__.py
• [ x ] API.rst is up to date, along with other sphinx docs pages
• [ x ] Example notebooks are rerun and differences in results scrutinized
• Updated changelog