Feat/database manager

[cardosofede]

This PR is adding a database manager class to improve the communication with the sqlite database.
Also, the logic of the trade fees was included in the strategy data class and in the graphs.
Minor improvements in graph style too.

[fengtality]

Approved, but note that I couldn't get past this UX issue:

Looks like I need to define a config file, but it's grayed out.

[cardosofede]

@fengtality is possible that you don't have trades available?

[fengtality]

is possible that you don't have trades available?

Yup, that DB has no trades. I suggest handling that case and display a message.

I would also add a note saying that it only works on Binance and Binance Futures currently, since it's tailored to their trading symbol format.

[fengtality]

works well on binance_paper_trade

[nikspz]

Tests performed:

• Cloned and install feature branch and PR6288
• conda env create -f environment_conda.yml
• conda activate streamlit-apps
• streamlit run main.py
• Copied URL to browser
• Created symlink with ln -s /path/to/hummingbot/data data
• Review Strategy Performance now shows fees in USDT for binance spot
• Confirmed fees amount is showing correct amount

Note: for binance perpetual there's ongoing issue on Strategy Performance tab with AttributeError: module 'ccxt' has no attribute 'binance_perpetual'

[nikspz]

Mentioned that ccxt will be removed in another PR