Is there any light client for Monero where I can create and import private keys/mnemonic-seed and send and receive transactions like electrum for Bitcoin / Dash ?
This addresses part of your question:
The lightwallet by jwinterm is probably most similar thing to an SPV wallet so far https://getmonero.org/getting-started/choose
shen-noether is working on a mobile wallet that will connect to a remote node https://hellomonero.com/tags/shen-noether
Jaxx and Exodus wallets are also in development
I assume you mean "light" to mean that the wallet does not keep a copy of the blockchain. Well, if you have a node to point the wallet at, whether it be a trusted external node or whether it be your little Raspberry Pi for example, then you can configure monero-wallet-cli to act as a light client. Actually, very little configuration is needed at all. See this post for how to do it on your internal network.
If you use monero-wallet-cli, it uses mnemonic seeds, and it has full wallet functionality (aside from it not currently having a GUI wrapped around it).